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Rapid morphological and genetic change in Chicago-area Peromyscus
Abstract
We report rapid change of morphology and mitochondrial genes in white-footed mice (Peromyscus leucopus) in the Chicago (Illinois, USA) region. We sequenced mitochondrial DNA COX2 from 55 museum skins of white-footed mice caught in the Chicago area since 1855 and from 44 mice recently trapped in the same locations. We found consistent directional genotype replacement at five separate collection locations. We later focused on a single one of these locations (Volo Bog State Natural Area) and sequenced mitochondrial D-loop control region from 58 museum skins of mice collected in 1903-1976 and 32 mice recently trapped there. We found complete and more recent replacement of D-loop haplotypes, apparently occurring between 1976 and 2001. We tested whether these genetic changes were mirrored by changes in morphology by comparing 15 external and cranial traits. We found no significant morphological differences between mice collected in 1903-1976; however, mice collected in 2001-2003 showed 9 of 15 measurements to be significantly changed relative to the earlier samples. Recent mice were longer in total length, with broader, longer noses, and longer but shallower skulls(1). Discriminant function analysis allowed for 100% correct classification using these traits. Principal components analysis shows variance over time is well distributed across both external and cranial measures. The sequential replacements of haplotypes and the rapid change of morphology can best be explained by replacement of the regional population with immigrants from genetically distinct neighbouring populations, likely facilitated by the large environmental changes occurring over the time period. Replacement with genotypes from external populations may be a common mechanism of evolution of newly adaptive local forms in an increasingly human-impacted world.
Supplementary resources (27)
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... Rapid morphological evolution has been documented in rodents (e.g. Wolf et al. 2009) and in Peromyscus in particular (Pergams and Ashley 1999;Pergams and Lacy 2008). Pergams and Lacy (2008) found an increase in body size in P. leucopus, as well as an increase in length and width of the rostrum and a decrease in the depth of the skull within 25 years in Chicago area; these morphological changes were accompanied by changes in the genetic structure of the population. ...
... Wolf et al. 2009) and in Peromyscus in particular (Pergams and Ashley 1999;Pergams and Lacy 2008). Pergams and Lacy (2008) found an increase in body size in P. leucopus, as well as an increase in length and width of the rostrum and a decrease in the depth of the skull within 25 years in Chicago area; these morphological changes were accompanied by changes in the genetic structure of the population. Interestingly, as at Mont Saint-Hilaire, this rapid morphological change coincided with a new selection pressure, the progressive replacement of P. maniculatus by P. leucopus Nyberg 2001, 2005;Pergams and Lacy 2008). ...
... Pergams and Lacy (2008) found an increase in body size in P. leucopus, as well as an increase in length and width of the rostrum and a decrease in the depth of the skull within 25 years in Chicago area; these morphological changes were accompanied by changes in the genetic structure of the population. Interestingly, as at Mont Saint-Hilaire, this rapid morphological change coincided with a new selection pressure, the progressive replacement of P. maniculatus by P. leucopus Nyberg 2001, 2005;Pergams and Lacy 2008). ...
We studied morphological variation in two closely related and ecologically similar species of mice of the genus Peromyscus, the deer mouse (P. maniculatus) and white-footed mouse (P. leucopus), over the last 50 years in Southern Quebec. We found that contemporary populations of the two species are distinct in morphology and interpret this differentiation as a reflection of resource partitioning, a mechanism favouring their local coexistence. While there was no size trend, geographic or temporal, both species displayed a concomitant change in the shape of their skull over the last 50 years, although this change was much more apparent in the white-footed mouse. As a result, the two species diverged over time and became more distinct in their morphology. The observed changes in morphology are large given the short time scale. During this period, there was also a shift in abundance of the two species in Southern Quebec, consistent with the northern displacement of the range of the white-footed mouse in the last 15 years. Our study thus reports the changes in morphology of two co-occurring mammal species that were accompanied by changes in distribution and local abundance, potentially in response to rapid climate change.
... Ранее митохондриальные гены считались нейтральными, что позволяло использовать их в качестве молекулярных часов, но сейчас показано -митохондриальный геном также может подвергаться действию отбора (Balloux, 2010;Oliveira et al., 2019). У обыкновенной белозубки (Crocidura russula) (Fontanillas et al., 2005) и белоногого хомячка (Pergams, Lacy, 2008) были обнаружены конкретные митохондриальные гаплотипы, которые связаны с более эффективным термогенезом и лучшей выживаемостью особей в зимний период (Fontanillas et al., 2005;Pergams, Lacy, 2008). ...
... Ранее митохондриальные гены считались нейтральными, что позволяло использовать их в качестве молекулярных часов, но сейчас показано -митохондриальный геном также может подвергаться действию отбора (Balloux, 2010;Oliveira et al., 2019). У обыкновенной белозубки (Crocidura russula) (Fontanillas et al., 2005) и белоногого хомячка (Pergams, Lacy, 2008) были обнаружены конкретные митохондриальные гаплотипы, которые связаны с более эффективным термогенезом и лучшей выживаемостью особей в зимний период (Fontanillas et al., 2005;Pergams, Lacy, 2008). ...
01.11.2022 г. После доработки 15.02.2023 г. Принята к публикации 20.02.2023 г. В обзоре, обобщающем собственные и литературные данные, на примере обыкновенного хомяка обсуждаются процессы, которые происходят в популяциях мелких млекопитающих при освоении ими городской среды. Исконно, обыкновенный хомяк был, по-видимому, связан с лесостепной зо-ной, но с развитием земледелия стал гемиагрофилом, заселяя окраины полей, что обеспечивало ему в течение года хорошую кормовую базу. Изменение культуры земледелия (замена фрагментарных полей на обширные площади пашен, занятых монокультурами, использование ядов и удобрений) способствовало тому, что оптимум вида сместился к территориям, занятым садами, огородами, а также урбоценозами. Это привело к изменениям генетической структуры популяций, большему (по сравнению с пригородом) разнообразию аллелей главного комплекса гистосовместимости, отвеча-ющих за устойчивость к патогенам, сокращению периода спячки вплоть до полного отказа от нее, снижению агрессивности к конспецификам, что позволяло на ограниченной территории устраи-вать большее количество нор и потреблять общие запасы. В качестве дополнительных кормовых ре-сурсов появилась возможность использования пищевых отбросов, что, возможно, привело к изме-нениям в пищеварительной системе и др. Все это позволяет обыкновенному хомяку успешно существо-вать в урбанизированной среде, несмотря на сокращение продолжительности жизни из-за большого количества стрессирующих факторов (паразитарная нагрузка, загрязнение и пр.). Предполагается, что не все перечисленные выше черты сформировались в процессе синурбанизации. Многие адаптации, приобретенные ранее, при освоении городской среды оказались эффективными. Очевидно, что путь, проделанный обыкновенным хомяком от экзоантропа к агрофилу и синурбисту, не уникален, многие другие виды млекопитающих и птиц прошли или проходят этот путь в настоящее время. Ключевые слова: мелкие млекопитающие, синурбанизация, урбоценоз, главный комплекс гистосов-местимости, спячка
... Changes in morphology within a short period are the product of microevolution via natural selection and/or phenotypic plasticity (Valladares et al. 2014;Pergams et al. 2015;Holmes et al. 2016). As many studies focus on highly polygenic traits, like body size, which are also susceptible to environmental influences, it is hard to determine whether these changes are genetically and/or plastically controlled (Pergams and Lacy 2007;Gardner et al. 2011). In any case, the power of environmental influence on RMC is undeniable. ...
... Many species of rodents are highly adaptable to fit in a world in constant land use and climatic changes (Auffray et al. 2009) and one of the ways of suitability seems to be RMC. Rates of change we found ranged from 1127.18d to 4308.62d, a similar range in cranial measurements for other cricetids, 586-5665d in Pergams and Lawler (2009), and 915-4772d in Pergams and Lacy (2007). Evolutionary rates are generally expected to be faster in warmer climates (Wright et al. 2006;Kozak and Wiens 2007), so we expected that rates of change would be greater than those of species that live in temperate zones. ...
Rapid Morphological Changes (RMCs) in rodents has been frequently documented. However, relation between RMCs and potential environmental drivers has been understudied. Here, we utilized a museum collection of four rodent species, collected in the same Atlantic Forest fragment, to investigate variation in the skull morphology over time, and test the influence of environmental and diversity drivers in RMC. We tested differences in size and shape of the skull between specimens collected in two temporal series, 1992–1997 and 2009–2010. For size, we tested differences over time in 20 cranial measurements within each species with independent-samples t-tests. To test shape variation, we performed a PERMANOVA with data generated by 13 landmarks on the dorsal view and another 13 on the ventral view throughout two-dimensional geometric morphometrics. We also explored the best relationships between cranial changes and five drivers of climate and two of rodent diversity by Akaike model selection. Our analysis showed RMCs in all studied species and theses changes were strongly influenced by tested drivers. The best model included only maximum temperature showing a negative association with size. Other tested models that presented similar fit showed that precipitation, humidity, richness of rodents, and minimum temperature had a positive association with size. Additionally, abundance also was negatively associated with morphological changes in the most abundant and the largest of the sampled species. The results indicated these species seem to quickly respond to environmental changes. Understanding which species have the potential to adapt to changes is central for the future of biodiversity conservation.
... within an urban or agricultural matrix (Munshi-South 2012; Munshi-South and Kharchenko 2010;Pergams and Lacy 2008;Wegner and Merriam 1990). ...
... ), such as Southern Québec(Desrosier et al. 2002). The generalist and opportunist behaviour of P. leucopus is suited to heterogeneous landscapes composed of a matrix of mixed urban and agricultural land use(Munshi-South 2012;Pergams & Lacy 2008;Wegner & Merriam 1990). The presence of fragmented landscapes of mixed land use in Southern Québec(Ruiz & Domon 2005;Wampach 1988) may not have hindered its expansion northward, but little is known about the factors that resist the movement of this important disease carrying species.A common parasite of the white-footed mouse, the black-legged tick (Ixodes scapularis), has also tracked climate change over the last few decades(Leighton et al. 2012;Ogden et al. 2006). ...
The white-footed mouse (Peromyscus leucopus) is a widespread habitat generalist species abundant over a large part of the North-American continent. In the past decade, due to climate and land use change, the range of this species has expanded northwards into Canada. The black-legged tick (Ixodes scapularis), is the vector of Lyme disease which also has tracked climate change over the last few decades. This may have been further promoted by the growing presence of P. leucopus, a favored host for the tick. Therefore, aspects of the landscape that affect the movement and distribution of the white-footed mouse, will also affect the expansion of the tick, and consequently the spread of Lyme disease. In this thesis, I first reviewed published results that relied on genetic and non- genetic biological data to investigate the influence of local habitat and landscape characteristics on the movement and dispersal patterns in the white footed-mouse. Next, I evaluated the relations between breeding habitat and landscape resistance against the genetic differentiation between 11 populations in Montérégie, Québec, Canada. I was able to simultaneously measure the effect of the habitat and the landscape on the genetic differentiation of these mouse populations by utilizing numerical optimization to fit a model to previously published genetic data. I used ecological distance computed from resistance surfaces with Circuitscape to infer the effect of the landscape. Concurrently, I estimated the habitat quality of our sampling localities and correlated these to relevant habitat measurements. I found that both characteristics within and between forest patches have more of an impact on genetic differentiation than the geographical distance between the mice populations. This suggests that this species can disperse and use a wide range of habitats, in accordance with its recent rapid expansion in the region.
... Our study emphasises the importance of museum collections to address questions that may not be easily tackled otherwise. For example, by using museum specimens collected over the last centuries we can investigate how populations respond over time to changing environmental conditions, e.g. the impact of anthropogenic disturbance (Pergams and Lacy 2008;Pergams and Lawler 2009;Snell-Rood and Wick 2013). We also want to highlight the importance of increasing the representation of urban populations in museum collections to facilitate the implementation of future studies that are not limited by low sample sizes, discontinuous time scales, or an unbalanced presence of specimens collected across gradients from highly urban to highly non-urban locations. ...
The expansion of urban environments and how animals may be affected by them are being increasingly investigated, leading to a surge in urban ecology studies. Many urban ecology studies involve a direct comparison between rural and urban populations, or the use of urban gradients along a continuum from rural to urban areas. The implicit, although not properly investigated, assumption in these rural vs urban comparisons is that the rural populations offer a control that represents a lack of the anthropogenic stressors affecting the urban populations. Here we used museum skulls from 14 rodent species to conduct two separate studies, measuring fluctuating asymmetry (FA) as a proxy of developmental stress to assess the effect of anthropogenic disturbance. First, we compared urban and rural specimens of Mus musculus (house mouse) to validate our methodological approach. Second, we compared rural specimens from 14 rodent species collected during the last two centuries across Austria. We hypothesised that FA in rural populations has not increased over the last two centuries, which would support the use of rural populations as a proper control in rural vs urban comparisons. We found higher morphological asymmetry in urban populations of Mus musculus compared to rural populations, which is consistent with similar studies in other species. However, we did not find any significant increase in FA over time in rural populations for any of the studied species. This offers some support to the common practice of using rural populations as a control in rural vs urban comparisons when assessing the effects of urbanisation.
... As a molecular genetic marker, a noncoding region (control region) of mtDNA was chosen, which has a high rate of accumulation of mutations and allows analyzing evolutionary processes at the population and intraspecific levels [31]. This marker is often used to analyze intraspecific and population variability both in the common vole [32][33][34][35][36] and in other mammals [37][38][39][40]. A recent study comparing the variability two mtDNA markers in a sibling species East European vole, M. arvalis s. str. ...
... В качестве молекулярно-генетического маркера был выбран некодирующий участок (контрольный регион) мтДНК, обладающий высокой скоростью накопления мутаций и позволяющий анализировать эволюционные процессы на популяционном и внутривидовом уровне [31]. Данный маркер часто используют для анализа внутривидовой и популяционной изменчивости как у серых полевок [32][33][34][35][36], так и у других млекопитающих [37][38][39][40]. Проведенное недавно исследование по сопоставлению изменчивости двух маркеров мтДНК у вида-двойника восточноевропейской полевки -M. ...
... Animals inhabiting warmer urban heat islands are predicted to be smaller in body size based on the general tendency for species to decrease in size with increasing temperature [17][18][19][20] . There is empirical support for urban heat island effects driving decreases in body size in various animal taxa, namely insects 21,22 , but limited support in endotherms 23 . Second, heterogeneity in urban areas can contribute to increased food resources and water availability compared to rural areas 24 , which could further mediate body sizes in urban areas (i.e., a resource rule 25 ). ...
Anthropogenically-driven climate warming is a hypothesized driver of animal body size reductions. Less understood are effects of other human-caused disturbances on body size, such as urbanization. We compiled 140,499 body size records of over 100 North American mammals to test how climate and human population density, a proxy for urbanization, and their interactions with species traits, impact body size. We tested three hypotheses of body size variation across urbanization gradients: urban heat island effects, habitat fragmentation, and resource availability. Our results demonstrate that both urbanization and temperature influence mammalian body size variation, most often leading to larger individuals, thus supporting the resource availability hypothesis. In addition, life history and other ecological factors play a critical role in mediating the effects of climate and urbanization on body size. Larger mammals and species that utilize thermal buffering are more sensitive to warmer temperatures, while flexibility in activity time appears to be advantageous in urbanized areas. This work highlights the value of using digitized, natural history data to track how human disturbance drives morphological variation.
... Animals inhabiting warmer urban heat islands are predicted to be smaller in body size based on the general tendency for species to decrease in size with increasing temperature [17][18][19][20] . There is empirical support for urban heat island effects driving decreases in body size in various animal taxa, namely insects 21,22 , but limited support in endotherms 23 . Second, heterogeneity in urban areas can contribute to increased food resources and water availability compared to rural areas 24 , which could further mediate body sizes in urban areas (i.e., a resource rule 25 ). ...
... Mismatch 438! resemble those presented here for NYC mice, indicating that mitochondrial selection during 440! urbanization may have been a general phenomenon throughout the range of P. leucopus. 441!Pergams & Lacy (2008) argued that these patterns in the Chicago area were due to replacement 442! of the original residents by migrants with a selective advantage; this scenario seems less likely 443! than selection on standing mtDNA variation in NYC because of the high isolation of NYC444! populations (Munshi-South 2012). The case for selection on mtDNA is further bolstered by our 445! ...
Severe fragmentation is a typical fate of native remnant habitats in cities, and urban wildlife with limited dispersal ability are predicted to lose genetic variation in isolated urban patches. However, little information exists on the characteristics of urban green spaces required to conserve genetic variation. In this study, we examine whether isolation in New York City (NYC) parks results in genetic bottlenecks in white-footed mice ( Peromyscus leucopus ), and test the hypotheses that park size and time since isolation are associated with genetic variability using nonlinear regression and information-theoretic model selection. White-footed mice have previously been documented to exhibit male-biased dispersal, which may create disparities in genetic variation between males and females in urban parks. We use genotypes of 18 neutral microsatellite data and four different statistical tests to assess this prediction. Given that sex-biased dispersal may create disparities between population genetic patterns inferred from bi- vs. uni-parentally inherited markers, we also sequenced a 324 bp segment of the mitochondrial D-loop for independent inferences of historical demography in urban P. leucopus . We report that isolation in urban parks does not necessarily result in genetic bottlenecks; only three out of 14 populations in NYC parks exhibited a signature of a recent bottleneck at 18 neutral microsatellite loci. Mouse populations in larger urban parks, or parks that have been isolated for shorter periods of time, also do not generally contain greater genetic variation than populations in smaller parks. These results suggest that even small networks of green spaces may be sufficient to maintain the evolutionary potential of native species with certain characteristics. We also found that isolation in urban parks results in weak to nonexistent sex-biased dispersal in a species known to exhibit male-biased dispersal in less fragmented environments. In contrast to nuclear loci, mitochondrial D-loop haplotypes exhibited a mutational pattern of demographic expansion after a recent bottleneck or selective sweep. Estimates of the timing of this expansion suggest that it occurred concurrent with urbanization of NYC over the last few dozens to hundreds of years. Given the general non-neutrality of mtDNA in many systems and evidence of selection on related coding sequences in urban P. leucopus , we argue that the P. leucopus mitochondrial genome experienced recent negative selection against haplotypes not favored in isolated urban parks. In general, rapid adaptive evolution driven by urbanization, global climate change, and other human-caused factors is underappreciated by evolutionary biologists, but many more cases will likely be documented in the near future.
... However, several studies have demonstrated that skeletal shape, i.e. the relative proportions and orientations of bony structures, can also undergo change in a short period of time (e.g. Pergams & Lacy, 2008;Nagorsen & Cardini, 2009;Franssen, 2011;Yazdi & Adriaens, 2011;Doudna & Danielson, 2015;Renaud et al., 2015). Such morphological changes resulting from evolution on islands or in habitat fragments may also have functional consequences. ...
Isolation due to habitat fragmentation can lead to morphological and functional variation between populations, with the effect being well documented in rodents. Here, we investigated whether such morphological variation could be identified between British populations of the Eurasian red squirrel (Sciurus vulgaris). This species was once widespread across Great Britain, but suffered a severe population decline across the 20th century, leaving a highly fragmented distribution. The aim was to test for morphological and biomechanical variation of the mandible between the remaining British red squirrel populations, and between British and continental European red squirrels. Linear and geometric morphometric methods were used to analyse shape in a sample of over 250 red squirrel hemi-mandibles from across Britain plus a sample from Germany representing the central European subspecies. Procrustes ANOVA identified significant shape variation between populations, with particularly distinct differences being noted between red squirrels from Germany and several British red squirrel populations, which may reflect their evolutionary history. Linear biomechanical measurements showed that the red squirrels from Formby and Jersey had a significantly lower mechanical advantage of the temporalis muscle than other British populations, suggesting they were less efficient at gnawing. This functional difference may be related to many factors, such as founder effect, potential inbreeding and/or past supplemental feeding with less mechanically resistant food items.
... and 2001 due to population replacement (Pergams & Lacy, 2008); similar to our work, the urban environment may not have changed much during this time, opening the question of what landscape processes facilitated replacement. A study of temporal change in fish body shape within urbanizing streams observed rapid change followed by maintenance of the new shape over time (Kern & Langerhans, 2018). ...
Urbanization exposes species to novel environments and selection pressures that may change morphological traits within a population. We investigated how the shape and size of crania and mandibles changed over time within a population of brown rats (Rattus norvegicus) living in Manhattan, New York, USA, a highly urbanized environment. We measured 3D landmarks on the cranium and mandible of 62 adult individuals sampled in the 1890s and 2010s. Static allometry explained approximately 22% of shape variation in crania and mandible datasets, while time accounted for approximately 14% of variation. We did not observe significant changes in skull size through time or between the sexes. Estimating the P‐matrix revealed that directional selection explained temporal change of the crania but not the mandible. Specifically, rats from the 2010s had longer noses and shorter upper molar tooth rows, traits identified as adaptive to colder environments and higher quality or softer diets, respectively. Our results highlight the continual evolution to selection pressures. We acknowledge that urban selection pressures impacting cranial shape likely began in Europe prior to the introduction of rats to Manhattan. Yet, our study period spanned changes in intensity of artificial lighting, human population density, and human diet, thereby altering various aspects of rat ecology and hence pressures on the skull.
... Inferences about relative and absolute maladaptation will sometimes correspond to each other, such as when climate warming causes a phenotype-environment mismatch (relative maladaptation) that generates population declines (absolute maladaptation; e.g., Both et al. 2006;Pörtner and Knust 2007;Willis et al. 2008) or when a resident population both is inferior to immigrants (relative maladaptation) and has a mean fitness below 1 (absolute maladaptation ;Saltonstall 2002;Pergams and Lacy 2007;Howells et al. 2012;Yampolsky et al. 2014). At other times, however, relative and absolute inferences will not correspond to each other (table 2), such as when residents in polluted environments have lower fitness than immigrants (relative maladaptation) yet the residents remain very abundant and successful (absolute adaptation; Brady 2013Brady , 2017Rolshausen et al. 2015;Rogalski 2017). ...
Evolutionary biologists have long trained their sights on adaptation, focusing on the power of natural selection to produce relative fitness advantages while often ignoring changes in absolute fitness. Ecologists generally have taken a different tack, focusing on changes in abundance and ranges that reflect absolute fitness while often ignoring relative fitness. Uniting these perspectives, we articulate various causes of relative and absolute maladaptation and review numerous examples of their occurrence. This review indicates that maladaptation is reasonably common from both perspectives, yet often in contrasting ways. That is, maladaptation can appear strong from a relative fitness perspective, yet populations can be growing in abundance. Conversely, resident individuals can appear locally adapted (relative to nonresident individuals) yet be declining in abundance. Understanding and interpreting these disconnects between relative and absolute maladaptation, as well as the cases of agreement, is increasingly critical in the face of accelerating human-mediated environmental change. We therefore present a framework for studying maladaptation, focusing in particular on the relationship between absolute and relative fitness, thereby drawing together evolutionary and ecological perspectives. The unification of these ecological and evolutionary perspectives has the potential to bring together previously disjunct research areas while addressing key conceptual issues and specific practical problems.
... Generation time in the study population has been estimated to be 263 days [14]. Species mean evolutionary rates of head and skull measurements in eight rodent species (and subspecies in the case of Peromyscus maniculatus) were used for comparison [28][29][30][31] (table 1). A onesample Wilcoxon's signed-rank test was used to compare the median evolutionary rates in darwins from the literature to that of the study population. ...
Similar phenotypic changes occur across many species as a result of domestication, e.g. in pigmentation and snout size. Experimental studies of domestication have concentrated on intense and directed selection regimes, while conditions that approximate the commensal and indirect interactions with humans have not been explored. We examine long-term data on a free-living population of wild house mice that have been indirectly selected for tameness by regular exposure to humans. In the course of a decade, this mouse population exhibited significantly increased occurrence of white patches of fur and decreased head length. These phenotypic changes fit to the predictions of the ‘domestication syndrome’.
... Rapid morphological changes were found in rodents in 20 museum series collected on four continentstrends included both increases and decreases in the 15 investigated morphological traits, with size increases documented slightly more frequently (Pergams and Lawler 2009). For example, 9 of 15 compared measurements significantly differed between samples of white-footed mice (Peromyscus leucopus (Rafinesque, 1818)) from 1903 to 1976 and 2001-2003: mice became longer in total length, with broader, longer noses, and longer but shallower skulls (Pergams and Lacy 2008). During the twentieth century, the greatest length of skull and zygomatic breadth increased in Japanese field mouse (Apodemus speciosus (Temminck, 1844)), while the interorbital region and the length of the upper cheek teeth row slightly increased in Pratt's vole (Eothenomys smithii (Thomas, 1905)) (Yom-Tov and Yom-Tov 2004). ...
Using museum materials and recently trapped specimens of field voles (Microtus agrestis (Linnaeus, 1761)) from Lithuania and Estonia, we assessed temporal and latitudinal trends in body and skull size, comparing the periods 1980–1996 and 2014–2016. We measured four body and 23 skull characters, size-adjusting them using the geometric mean procedure. A pronounced decrease in the size of M. agrestis was noted in Estonia, where 23 out of 27 adjusted body and skull characters had decreased by up to 21.9%, with only the tail length, hind foot length, maximum height of mandibula excluding coronoid process and coronoid height of mandibula increasing significantly. Decreases were less marked in voles from Lithuania – most pronounced were a 6.1% decrease in adjusted body length, an 11.6% decrease in adjusted length of the braincase, a 3.85% decrease in the breadth of the braincase, measured at the widest part, a 2.9% decrease in condylobasal skull length and a 2.2% decrease in the height of the braincase. The coronoid height of the mandibula of Lithuanian individuals showed an 8.4% size increase. In both countries, the confounding effect of sex on the size changes of M. agrestis from 1980 to 2016 was much smaller than the effect of time period. Concluding, voles in Estonia became significantly smaller, while changes in the measured characters in Lithuania were heterogeneous.
... However, to date only a few studies have analyzed recent changes in body mass for this mega-diverse group and these works suggest that most rodent species are increasing in size, which deviates from both theoretical expectations (e.g. the energetic argument behind the Bergmann's rule) and empirical evidence for other endotherms. For example, studies analyzing temporal changes in (skull) size during (at least) the last four decades indicate that a reduction in size occurred in Peromyscus maniculatus (Pergams and Ashley 1999), no changes occurred in Eothenomys kageus and Otospermophilus beecheyi (Yom-Tov and Yom-Tov 2004), and an increase occurred in Apodemus speciosus, Callospermophilus lateralis, Urocitellus beldingi, Peromyscus leucopus and Rattus rattus (Yom-Tov and Yom-Tov 2004, Pergams and Lacy 2008, Eastman et al. 2012, Pergams et al. 2015. That is, the number of species that increased size was nearly double the species that did not change or reduced size. ...
A reduction in body size has been proposed as the third universal ecological response to global warming, after species distributional shifts and phenological changes. However, some recent studies raise doubts about the validity of this pattern, in particular for endotherms. Within this context, here we analyzed data on body mass (mb) for 17 rodent species, covering (at least) the last six decades, together with data on temperature change and basal metabolic rate (BMR) for each species. We found that: 1) ten species (58.8%) showed no significant changes in mb, while the remaining seven species (41.2%) decreased their size during the 20th century; 2) phylogenetic generalized linear mixed models indicate that there is a significant and negative effect of the year of collection on mb; 3) the correlation coefficient between mb and the year of collection (ryear) was not correlated with species mean mb, species distributional range, the length of the time series, or the change in ambient temperature; and 4) the correlation between ryear and (residual) BMR was significant (and negative) only for species that do not use torpor. In summary, our results suggest that reductions in mb are common among rodents, but we were unable to identify a clear cause behind these changes (e.g. some results support the energetic argument behind the Bergmann rule but other do not). We concluded that with less than 0.5% of the extant (known) rodent species analyzed to date, we still are far from reaching a clear understanding of current patterns of variation in body size that are associated with global environmental change for this group.
... Insular differentiation provided numerous models of pronounced morphological differentiation questioning the respective role of adaptation and random factors (Cardini et al. 2007a;Michaux et al. 2007b; Renaud and Auffray 2010;. Even contemporary evolution and response to current anthropic changes can find a morphological signature in rodents (Pergams and Lacy 2008;. ...
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
... These findings that NYC populations are genetically isolated but still maintain high levels of neutral genetic variation [36][37][38] indicated that the conditions for local adaptation to urban conditions may be widespread for white-footed mice and other urban Peromyscus [39]. Indeed, temporal replacement of mitochondrial haplotypes had previously been reported for Chicago-area P. leucopus, suggesting rapid evolution in urban populations [40,41]. ...
Deer mice in the genus Peromyscus occupy nearly every terrestrial habitat in North America, and have a long history as subjects of behavioral, ecological, evolutionary, and physiological study. Recent advances in transcriptomics, the study of the complete set of RNA transcripts produced by certain cell types or under certain conditions, have contributed to the development of Peromyscus as a model system. We review the recent use of transcriptomics to investigate how natural selection and gene expression plasticity contribute to the existence of deer mice in challenging environments such as highlands, deserts, and cities across North America. Transcriptomics also holds great promise for elucidating the genetic basis of mating systems and other behaviors in Peromyscus, but has to date been underutilized for developmental biology and disease studies. Future Peromyscus studies should apply robust comparative frameworks to analyze the transcriptomics of multiple populations of the same species across varying environmental conditions, as well as multiple species that vary in traits of interest.
... Peromyscus leucopus are abundant across North America, have a typically short lifetime dispersal capability of approximately 100 m, prefer oak-hickory secondary forests and consume a diet of arthropods, fruits, nuts, vegetation and fungus. White-footed mice are abundant in small, fragmented urban forests [14][15][16] and exchange migrants only through vegetated corridors between isolated NYC parks [17]. Substantial genetic structure at microsatellite loci exists between NYC parks [8], and there is evidence of divergence and selection in genes underlying functional traits in urban populations [18]. ...
How urbanization shapes population genomic diversity and evolution of urban wildlife is largely unexplored. We investigated the impact of urbanization on white-footed mice, Peromyscus leucopus, in the New York City (NYC) metropolitan area using coalescent-based simulations to infer demographic history from the site-frequency spectrum. We assigned individuals to evolutionary dusters and then inferred recent divergence times, population size changes and migration using genome-wide single nucleotide polymorphisms genotyped in 23 populations sampled along an urban-to-rural gradient. Both prehistoric climatic events and recent urbanization impacted these populations. Our modelling indicates that post-glacial sea-level rise led to isolation of mainland and Long Island populations. These models also indicate that several urban parks represent recently isolated P. leucopus populations, and the estimated divergence times for these populations are consistent with the history of urbanization in NYC.
... Changes in skull morphology were more pronounced for the Yosemite transect, indicating that as with the dietary analyses, relationships between environment and phenotype varied geographically. Rapid morpho-logical change associated with climatic conditions has been observed in a diverse array of rodents (Hendry et al., 2008;Pergams & Lacy, 2008;Pergams & Lawler, 2009;Eastman et al., 2012), with high-elevation species tending to display increases in body size (Ozgul et al., 2010;Eastman et al., 2012). Although we observed an increase in body size for T. alpinus in Yosemite, the converse was observed for this species in the Southern Sierras transect, thereby underscoring the variability and habitat-specific nature of phenotypic responses to environmental change. ...
Predicting how individual taxa will respond to climatic change is challenging, in part because the impacts of environmental conditions can vary markedly, even among closely related species. Studies of chipmunks (Tamias spp.) in Yosemite National Park provide an important opportunity to explore the reasons for this variation in response. While the alpine chipmunk (T. alpinus) has undergone a significant elevational range contraction over the past century, the congeneric and partially sympatric lodgepole chipmunk (T. speciosus) has not experienced an elevational range shift during this period. As a first step toward identifying the factors underlying this difference in response, we examined evidence for dietary changes and changes in cranial morphology in these species over the past century. Stable isotope analyses of fur samples from modern and historical museum specimens of these species collected at the same localities indicated that signatures of dietary change were more pronounced in T. alpinus, although diet breadth did not differ consistently between the study species. Morphometric analyses of crania from these specimens revealed significant changes in cranial shape for T. alpinus, with less pronounced changes in shape for T. speciosus; evidence of selection on skull morphology was detected for T. alpinus but not T. speciosus. These results are consistent with growing evidence that T. alpinus is generally more responsive to environmental change than T. speciosus but emphasize the complex and often geographically variable nature of such responses. Accordingly, future studies that make use of the taxonomically and spatially integrative approach employed here may prove particularly informative regarding relationships between environmental conditions, range changes, and patterns of phenotypic variation. This article is protected by copyright. All rights reserved.
... Work by Réale et al. (2003) demonstrated that shifts toward earlier breeding phenology in response to climate-induced changes in food supply are the result of both phenotypic plasticity (87 percent of the change) and an evolutionary response (13 percent). Recent work by Pergams and Lacy (2008) documented rapid genetic and morphological changes in Chicago-area mice (Peromyscus leucopus), though the mechanism for this change likely includes a complex set of environmental factors, in addition to recent climate changes. ...
... Like all bony structures, the cranium responds to variation in nutrition and the physical forces that load bone (Van der Klaauw, 1948;Moore, 1981;Herring, 1993;Ram ırez Rozzi et al., 2005;Hallgr ımsson et al., 2007;Gonzalez et al., 2014) and thus changes in environmental variables that affect the function of the skull may drive changes in cranial morphology. Multiple studies have reported relationships between cranial morphological variation and environmental conditions , 2013Pergams and Lacy, 2007;Pergams and Lawler, 2009;Grieco and Rizk, 2010;Yom-Tov and Geffen, 2011;Tomassini et al., 2014). Potential selective forces contributing to these relationships include habitat fragmentation (Pertoldi et al., 2006), invasive species (Viranta and Kauhala, 2011), and climate change (Pergams and Lawler, 2009). ...
Determining how species respond to prolonged environmental change is critical to understanding both their evolutionary biology and their conservation needs. In general, organisms can respond to changing environmental conditions by moving, by adapting in situ, or by going locally or globally extinct. Morphological changes, whether plastic or adaptive, are one way that species may respond in situ to local environmental change. Because cranial morphology is influenced by selective pressures arising from an organism's abiotic and biotic environments, including aspects of thermal physiology, diet, and sensory ecology, studies of cranial morphology may generate important insights into how species are responding to environmental change. To assess potential response of deer mice (Peromyscus maniculatus) to changing conditions in the Sierra Nevada Mountains of California, we quantified cranial variation in museum specimens of this species collected approximately 100 years apart. Specifically, we examined how cranial morphology varies in three populations of this geographically widespread , ecological generalist over elevation and time. Our analyses indicate that cranial morphology does not differ with elevation within either modern or historical samples but does vary between time periods, suggesting that in situ responses to environmental change have occurred. Contrary to predictions based on Berg-mann's rule, we found no consistent relationship between body size and either elevation or time, suggesting that morphological differences detected between historic and modern specimens are specific to factors influencing cranial structure. Collectively, these analyses demonstrate the potential importance of in situ changes in morphology as a response to changing environmental conditions.
... There are also studies on size or weight changes in extant mammals on a shorter, non-geological time scale (about one century or more). For rodents, Pergams & Lawler (2009) indicated changes in several characters of diverse rodents within the last 100+ years and fast changes were also indicated in the sigmodontine murid Peromyscus (Pergams & Lacy 2008). Changes in skull morphology over time have been demonstrated in the skull of the Arctic wolf (like overall reduction in overall size, size of the teeth, widening of the cranium and shortening of the facial region within about 60 years, Clutton-Brock et al. 1994). ...
The question whether the European wildcat, adapted to cooler climate than other small to medium sized felids, shows changes in body mass or size in response to climate change as indicated for other animals is addressed. The literature yielded body mass data of individual specimens covering the time span from about 1860 to 1960 Also the records of collections were accessed to record weight and body length. These mainly cover the time after 1950 Additionally, three cranial measures, gsl, cbl and zw were measured as indicators of size in the collections representing Germany and Slovakia. Museum records of weight from the last 60 years alone do not show a statistically significant change over time or mean annual temperature. But they do so for body length. The combined data from literature and collections from both regions show a statistically significant decrease in weight over time. As the samples from the literature and museum records represent different time periods, prior to and after 1950, it is difficult to decide if the literature data might be unrealistically high or if there was a real decrease in weight. The German and Slovakian samples differ statistically in the studied parameters, which complicates the picture. Overall the indications of changes in size of wildcats with time or mean annual temperature are not consistent in the studied regions and therefore difficult to assess. Even though there is ample material and substantial literature the collected specimens in the collections do mainly represent relatively short time periods and the available data on weight are also unevenly distributed in time. This supports the necessity to collect large series of specimens over time.
Mammals are predicted to vary in body size following Bergmann’s rule, with individuals found at higher latitudes in colder temperatures being larger in size compared to conspecifics occurring at lower latitudes in warmer temperatures. Body size is similarly expected to vary temporally, with a decrease in size through time due to recent climate warming. While Bergmann’s rule is well-supported in mammals, there is increasing evidence of exceptions to the rule. Here, we present patterns of size variation in 17 North American mammal species using five morphological traits (condylobasal skull length, skull width, maxillary toothrow length, body weight, and head-and-body length) to determine if size varies predictably for each species in space and time. We found little support for a widespread Bergmannian pattern for these species at a broad spatial scale (across North America) and a contemporary temporal scale (the past 120 years). The effects of latitude or year on each trait were highly variable with three types of responses: an increase, a decrease, or no change in size across space or through time. Spatial size trends were detected more often than temporal size trends, as the temperature range was significantly larger in space than through time. Body weight (the most variable trait) and head-and-body length were more likely to conform to Bergmann’s rule than craniodental measurements. We did not detect any changes in size variability with latitude, and our study species either increased or decreased in size variability over time. Our findings demonstrate that size variation in mammals is highly context-dependent. As such, caution is needed when using rules of body size variation to predict the future response of species to climate warning while valid in theory, it is likely too simplistic of an approach.
Specimen‐based data have played a central role in documenting body‐size shifts as a possible response to global warming over the last century. Identification of the drivers and patterns of these trends requires comparisons across taxa, often through meta‐analyses; however, a lack of repeatability within and interoperability (i.e. the potential for a dataset to be augmented for future research) among published studies is a major obstacle.
We reviewed published studies on mammal body‐size changes in the Anthropocene, focusing on those that used museum specimens to analyse body‐size trends over time in at least one species. We assessed these papers for repeatability and interoperability with the following criteria: raw data and specimen identifiers were published and accessible, measurements were unambiguously defined, and potential sex‐ and age‐based size differences among individuals were accounted for.
Most published body‐size studies have low potential for replication or augmentation; only one of 27 met all of our criteria. Although these 27 papers collectively generated an estimated 51,790 new body‐size measurements, only 1.25% (649) could be repeated or readily used in further investigations, as the remainder did not include raw data and/or specimen identifiers.
Based on these findings, we recommend the following best practices in the study of body‐size trends. First, authors should explicitly define and justify all measures of size and quantify measurement error and publish all data, including measurements and specimen catalogue numbers. In addition to complying with the fundamental scientific tenet of repeatability, this minimizes redundant handling and the concomitant risk of damage to irreplaceable and often fragile museum specimens. Second, authors should test and account for the effects of demography, as some dimensions can change throughout an individual's life. Adopting these practices will improve the quality of body‐size studies, enhance the utility of extended specimen data from natural history collections, and enable researchers to conduct more expansive investigations of size trends over time.
Island rule describes the graded trend of gigantism in small-bodied species to dwarfism in large-bodied species inhabiting islands, but causal explanations remain unresolved. We used geometric morphometrics to quantify cranial morphology of 544 meadow vole Microtus pennsylvanicus samples across 11 island and 3 mainland populations from the Outer Lands of New England (Atlantic) and the Alexander Archipelago of Alaska (Pacific). We compared the thermoregulation and endurance (TRE) and ecological release (ER) hypotheses using all-subsets linear models employing residual randomization permutation procedures (rrpp), and Akaike information criterion (AIC) for model selection. We decoupled direct and indirect effects of island variables on size using path analysis. We evaluated shape with principal components analysis (PCA) and Procrustes ANOVA on Procrustes shape coordinates, then assessed the impact of static allometry and TRE and ER variables on shape. Six Atlantic island populations exhibit significant signals of gigantism with the largest voles occurring on the smallest islands lacking predators. ER explains 63% of cranial size differences. Island area has a significant total effect on size by influencing the number of mammalian predators, resulting in a 0.011 increase in unit centroid size for a 100 km² decrease in island area. This corresponds to a predicted 0.9% change in size for every 100 km². Given static allometry, cranial shape does not respond to insularity independent of size. These results suggest that island rule is a latent evolutionary process whose manifestation depends on nuanced biogeographic and ecological contexts that have important conservation and taxonomic implications.
The expansion of urban environments and how animals may be affected by them are being increasingly investigated, leading to a surge in urban ecology studies. Many urban ecology studies involve a direct comparison between rural and urban populations, or the use of urban gradients along a continuum from rural to urban areas. The implicit, although not properly investigated, assumption in these rural vs urban comparisons is that the rural populations offer a control that represents a lack of the anthropogenic stressors affecting the urban populations. Here we used museum skulls from 14 rodent species to conduct two separate studies, measuring fluctuating asymmetry (FA) as a proxy of developmental stress to assess the effect of anthropogenic disturbance. First, we compared urban and rural specimens of house mice ( Mus musculus ) to validate our methodological approach. Second, we compared rural specimens from 14 rodent species collected during the last two centuries across Austria. We hypothesised that FA in rural populations has not increased over the last two centuries, which would support the use of rural populations as a proper control in rural vs urban comparisons. We found higher morphological asymmetry in urban populations of Mus musculus compared to rural populations, which is consistent with similar studies in other species. However, we did not find any significant increase in FA over time in rural populations for any of the studied species. This supports the common practice of using rural populations as a control in rural vs urban comparisons when assessing the effects of urbanisation.
The white-footed deer mouse (Peromyscus leucopus) and the North American deer mouse (P. maniculatus) are widely distributed throughout North America, often with overlapping distributions. These species are believed to be sympatric east of the Balcones fault zone in Texas, but records from natural history collections indicate that P. maniculatus is not common from this region. Given that these two species are notoriously difficult to differentiate morphologically, it is possible that specimens have been incorrectly identified and that P. maniculatus may be rare or not present in East Texas. This study aims to determine if P. leucopus and P. maniculatus can be differentiated morphologically east of the Balcones fault zone in Texas. Cranial and external characters from genetically identified specimens representing each species were analyzed using traditional and geometric morphometric methods. Morphological analyses revealed that genetically identified specimens of P. leucopus and P. maniculatus from east of the Balcones fault zone could be differentiated using a suite of morphological characters. Many of the specimens of P. leucopus used in this study were originally misidentified, suggesting that P. maniculatus is rare in East Texas.
Warming climate and increasing desertification urges the identification of genes involved in heat- and dehydration-tolerance to better inform and target biodiversity conservation efforts. Comparisons among extant desert adapted species can highlight parallel or convergent patterns of genome evolution through the identification of shared signatures of selection. We generate chromosome-level genome assembly for the canyon mouse (Peromyscus crinitus) and test for signature of parallel evolution by comparing signatures of selective sweeps across population-level genomic resequencing data from another desert specialist deer mouse (P. eremicus) and a widely-distributed habitat generalist (P. maniculatus), that may be locally adapted to arid conditions. We identify few shared candidate loci involved in desert adaptation and do not find support for a shared pattern of parallel evolution. Instead, we hypothesize divergent molecular mechanisms of desert adaptation among deer mice, potentially tied to species-specific historical demography, which may limit or enhance adaptation. We identify a number of candidate loci experiencing selective sweeps in the P. crinitus genome that are implicated in osmoregulation (Trypsin, Prostasin) and metabolic regulation (Kallikrein, eIF2-alpha kinase GCN2, APPL1/2), which may be important to accommodating hot and dry environmental conditions.
Urbanization significantly alters natural ecosystems and has accelerated globally. Urban wildlife populations are often highly fragmented by human infrastructure, and isolated populations may adapt in response to local urban pressures. However, relatively few studies have identified genomic signatures of adaptation in urban animals. We used a landscape genomics approach to examine signatures of selection in urban populations of white-footed mice ( Peromyscus leucopus ) in New York City. We analyzed 154,770 SNPs identified from transcriptome data from 48 P. leucopus individuals from three urban and three rural populations, and used outlier tests to identify evidence of urban adaptation. We accounted for demography by simulating a neutral SNP dataset under an inferred demographic history as a null model for outlier analysis. We also tested whether candidate genes were associated with environmental variables related to urbanization. In total, we detected 381 outlier loci and after stringent filtering, identified and annotated 19 candidate loci. Many of the candidate genes were involved in metabolic processes, and have well-established roles in metabolizing lipids and carbohydrates. Our results indicate that white-footed mice in NYC are adapting at the biomolecular level to local selective pressures in urban habitats. Annotation of outlier loci suggest selection is acting on metabolic pathways in urban populations, likely related to novel diets in cities that differ from diets in less disturbed areas.
The tropical bioregion of Sundaland, Southeast Asia, is a major hotspot of world
biodiversity, including mammal biodiversity. Its complex geological history lays out an
excellent scenario to study evolution. However, the interpretations of Sunda
biogeography patterns for this group has been limited due to (1) uncertainties in
taxonomy, and (2) biased and incomplete sampling of certain regions (e.g. Sumatra). I
combined a taxonomic approach followed with extensive sampling in the field and from
natural history collections for well-represented groups of rats (Sundamys and Rattus) as
models to evaluate the interplay of Plio-Pleistocene changes in the diversification
patterns of mammals in Sundaland. I use genetics in combination with morphology and
ecology to look at diversification both within and between species in these two related
genera to test biogeographic and other evolutionary hypotheses.
Body size decline is hypothesized to be a key response to climate warming, including warming driven by urban heat islands. However, urbanization may also generate selective gradients for body size increases in smaller endotherms via habitat fragmentation. Here we utilize a densely sampled, multi-source dataset to examine how climate and urbanization affect body size of Peromyscus maniculatus (PEMA), an abundant rodent found across North America. We predicted PEMA would conform to Bergmann’s Rule, e.g. larger individuals in colder climates, spatially and temporally. Hypotheses regarding body size in relation to urbanization are less clear; however, with increased food resources due to greater anthropogenic activity, we expected an increase in PEMA size. Spatial mixed-models showed that PEMA conform to Bergmann’s Rule and that PEMA were shorter in more urbanized areas. With the inclusion of decade in mixed-models, we found PEMA mass, but not length, is decreasing over time irrespective of climate or population density. We also unexpectedly found that, over time, smaller-bodied populations of PEMA are getting larger, while larger-bodied populations are getting smaller. Our work highlights the importance of using dense spatiotemporal datasets, and modeling frameworks that account for bias, to better disentangle broad-scale climatic and urbanization effects on body size.
Urbanization significantly alters natural ecosystems and has accelerated globally. Urban wildlife populations are often highly fragmented by human infrastructure, and isolated populations may adapt in response to local urban pressures. However, relatively few studies have identified genomic signatures of adaptation in urban animals. We used a landscape genomics approach to examine signatures of selection in urban populations of white-footed mice (Peromyscus leucopus) in New York City. We analyzed 154,770 SNPs identified from transcriptome data from 48 P. leucopus individuals from three urban and three rural populations, and used outlier tests to identify evidence of urban adaptation. We accounted for demography by simulating a neutral SNP dataset under an inferred demographic history as a null model for outlier analysis. We also tested whether candidate genes were associated with environmental variables related to urbanization. In total, we detected 381 outlier loci and after stringent filtering, identified and annotated 19 candidate loci. Many of the candidate genes were involved in metabolic processes, and have well-established roles in metabolizing lipids and carbohydrates. Our results indicate that white-footed mice in NYC are adapting at the biomolecular level to local selective pressures in urban habitats. Annotation of outlier loci suggest selection is acting on metabolic pathways in urban populations, likely related to novel diets in cities that differ from diets in less disturbed areas. This article is protected by copyright. All rights reserved.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
Ground squirrels of the genus Marmota are known for their ability to tolerate bitterly cold climates, which they in part accomplish with their exceptional ability to hibernate for as much as eight months a year (Armitage et al., 2003). Most of the 15 living species are associated with montane habitats, and those that are not, like the North American woodchuck (Marmota monax) and the eastern European and central Asian bobak (M. bobak) inhabit regions with strongly seasonal climates and often bitterly cold winters (Armitage, 2000) (Figure 9.1). All marmots construct burrows, which can be more than one metre deep even in comparatively mild climates and as much as seven metres deep in the harsh climates of the Himalayas (Barash, 1989). During the cold phases of the last half of the Quaternary the fossil record demonstrates many marmots inhabited periglacial environments (Zimina and Gerasimov, 1973; Kalthoff, 1999). For these reasons, marmots are sometimes considered to be a quintessentially Quaternary clade, specialists on the cold variable climates that are unique to the past 2.6 million years of Earth’s history. The world in which they originated, however, was very different; a warmer one in which there were no tundra biomes, no glacial-interglacial cycles, and no permanent ice cover in the Northern Hemisphere. In this chapter, we review the fossil and phylogenetic history of marmots, the palaeoenvironments in which they originated, and their relationship to glacial-interglacial cycles to better understand the contexts in which the specializations of this unique clade of rodents arose. The Quaternary, the current geological period, is defined by the onset of permanent ice sheets in the Northern Hemisphere 2.58 million years ago and is by far the coldest period since the extinction of the last non-avian dinosaurs 65 million years ago (Zachos et al., 2001; Gibbard et al., 2010).
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
Genetic studies have shown that New York City white-footed mouse (Peromyscus leucopus) populations exhibit substantial genetic structure and high levels of allelic diversity and heterozygos-ity. These studies have also identified mutations and genes involved in the divergence of urban and rural P. leucopus populations. To investigate whether morphological change mirrors the genetic differentiation observed in New York City P. leucopus populations, we conducted univariate and multivariate analyses on 4 external and 14 skull variables to compare urban, suburban and rural P. leucopus populations from in and around New York City. The only significant morphological differences among the three populations were in upper and lower toothrow lengths, both of which had high loadings in our principal components analyses. In general, rural individuals were found to have longer upper and lower toothrows than urban ones. This difference is likely due to the relationship between food quality and size of dental occlusal surfaces. Generally, lower-quality food requires more chewing and its consumption is facilitated by larger occlusal surfaces. Our results suggest that urban mice consume a higher-quality diet or food that requires less chewing than their rural counterparts by making use of the availability of natural food sources in rich, vegetative understories characteristic of urban forest fragments. Our cluster analysis of the skull variables revealed that urban and suburban populations are more similar to one another than to the rural population.
This study aimed to evaluate the advantages and disadvantages of the use of different types of biological samples obtained by non-invasive sampling techniques, in the genetic study of mammal populations. Samples of scats, hair, soft tissues of dead animals and furs and bones from museum specimens were used to evaluate different protocols of DNA extraction and PCR amplification of several mitochondrial DNA fragments in three species of mammals. The efficiency of each procedure wasevaluated qualitatively in terms of sampling simplicity, the yield of the amplifications, and costs and time employed in the processing of samples. Results indicate that obtaining genetic data from non-invasive sampling techniques can be economically costly and laborious, but the sampling simplicity compared with conventional methods, the diminution of the animals' stress, and the efficiency in obtaining data, would validate these techniques as an acceptable alternative for genetic studies.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
Recently, there has been a growing interest for rapid evolution and its potential role in ecological processes. For example, it has been hypothesized that rapid adaptation is a factor favoring the establishment of invasive species in new environments. If this hypothesis is true, it could have implications in the management and prevention of biological invasions. In vertebrates, lots of studies report cases of rapid phenotypic changes in invasive species following their introduction in a novel environment. However, because of the difficulties of directly testing for adaptation, very few of them were able to prove that these phenotypic changes result from rapid adaptation. In this thesis, we were thus interested in assessing whether rapid adaptation can explain phenotypic changes observed in recently introduced populations. Instead of directly testing for adaptation, we tested for alternative hypotheses, which are easier to investigate. Indeed, a phenotypic difference observed between populations established in different environments can be caused by natural selection but also by phenotypic plasticity, by a different phylogenetic origin and by stochastic evolution (i.e. stochastic changes in allele frequencies in a population as the result of demographic processes such as founder effects and bottlenecks). Here, we studied two successful invasive bird species introduced in several kinds of environments. We described the morphology of individuals in these populations, and tested for the effects of historical factors (i.e. phylogenetic origin and recent demographic history) to explain morphological differences observed between populations. In both species, our results show that stochastic evolution resulting of recent demographic history is likely to be the cause of the morphological differences observed. This was true for all the cases we studied except one. In this last case, neither a difference in phylogenetic origin, nor stochastic evolution could explain de phenotypic differences observed between two environments. It is therefore possible that rapid adaptation occurred in this case but the hypothesis of phenotypic plasticity remains to be tested. In conclusion, with this work we highlighted that recent demographic processes can have an important role in causing morphological differentiation in invasive species. This role was probably underestimated in studies on rapid adaptation and should be taken into account in the future. We also showed that the comparative approach we used can allow identifying possible cases of rapid adaptation by first rejecting alternative hypotheses.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
We evaluate methods for measuring and specifying rates of microevolution in the wild, with particular regard to studies of contemporary, often deemed "rapid," evolution. A considerable amount of ambiguity and inconsistency persists within the field, and we provide a number of suggestions that should improve study design, inference, and clarity of presentation. (1) Some studies measure change over time within a population (allochronic) and others measure the difference between two populations that had a common ancestor in the past (synchronic). Allochronic studies can be used to estimate rates of "evolution," whereas synchronic studies more appropriately estimate rates of "divergence." Rates of divergence may range from a small fraction to many times the actual evolutionary rates in the component populations. (2) Some studies measure change using individuals captured from the wild, whereas others measure differences after rearing in a common environment. The first type of study can be used to specify "phenotypic" rates and the later "genetic" rates. (3) The most commonly used evolutionary rate metric, the darwin, has a number of theoretical shortcomings. Studies of microevolution would benefit from specifying rates in standard deviations per generation, the haldane. (4) Evolutionary rates are typically specified without an indication of their precision. Readily available methods for specifying confidence intervals and statistical significance (regression, bootstrapping, randomization) should be implemented. (5) Microevolutionists should strive to accumulate time series, which can reveal temporal shifts in the rate of evolution and can be used to identify evolutionary patterns. (6) Evolutionary rates provide a convenient way to compare the tempo of evolution across studies, traits, taxa, and time scales, but such comparisons are subject to varying degrees of confidence. Comparisons across different time scales are particularly tenuous. (7) A number of multivariate rate measures exist, but considerable theoretical development is required before their utility can be determined. We encourage the continued investigation of evolutionary rates because the information they provide is relevant to a wide range of theoretical and practical issues.
A total of 383 Peromyscus was collected from southern Illinois to determine morphological characteristics useful in identifying individuals as either P. leucopus (Rafinesque, 1818) or P. maniculatus (Wagner, 1845). Polyacrylamide gel electrophoresis of salivary amylase was used to positively identify all specimens. No univariate morphological character accurately discriminated between the two species because of a high degree of intraspecific variation. Stepwise discriminant function analysis of external characters correctly classified 97.9% of subadults to species. The most important external character was the tail length/body length ratio. This ratio was also the most important factor in discrimination of adults; the function correctly classified 98.6% of individuals. Considering skull measurements of adults, 9 cranial characters were needed to differentiate between the two species, with a correct classification of 98.9%. For old adults, all specimens were classified correctly using 5 cranial characters. There was no fast, easy, accurate method to discriminate between these species 100% of the time in the field.
External features of the tail and pelage, and quantitative cranial characteristics were used to discriminate Peromyscus leucopus from P. maniculatus (n = 204) from northeastern North America. Species assignments were based on the phenotype of salivary amylase. Characteristics of the pelage and tail yielded correct identification of 55% of adult specimens. A previously published discriminant-function equation based on 11 cranial measurements correctly classified 66% of adults and 56% of specimens of all age classes. Two new discriminant equations were generated based on 12 and 11 skull measurements, respectively. The first equation correctly classified 100% of skulls in two separate datasets (n = 164; n = 50), and the second correctly classified 94% in a single dataset (n = 195).
We report on the evolutionary change in bill size of a species of Hawaiian honeycreeper resulting from an apparent dietary shift caused by dramatic declines and extinctions of lobelioids, a historically favored nectar source. Although it now feeds mainly on the flowers of the ohia tree (Metrosideros polymorpha), early Hawaiian avifaunal accounts report that the i’iwi (Vestiaria coccinea), which has a long decurved bill, fed primarily on the flowers of Hawaiian Lobelioideae, which typically have long decurved corollas. A coevolutionary association of i’iwi bill and flower morphology has often been asserted. We test the hypothesis that the shift in the i’iwi’s diet from the long corolla lobelioid flowers to ohia flowers, which lack corollas, resulted in directional selection for shorter bills. We evaluate this hypothesis by comparing the morphological characters of museum specimens from the island of Hawaii collected before 1902 with recent specimens from the Hakalau National Wildlife Refuge, Hawaii. We examine evidence of change in morphological characters using multivariate analysis and a nonparametric cubic spline technique. Results from all analyses are congruent: bill length is shorter in recent specimens.
The prairie deer mouse (Peromyscus maniculatus bairdii ) was more common than the white-footed mouse (P. leucopus) in museum collections from the 6 Illinois counties of the Chicago region before 1920 but constitutes only 5% of specimens deposited since 1970. Because white-footed mouse prefers woody vegetation and because prairie deer mouse is limited to prairie or large open habitats, the change in proportion is likely driven by a disproportionate loss of prairie among remaining natural habitat and increases in woody vegetation within grasslands. The decline of the prairie vole ( Microtus ochrogaster) relative to the meadow vole (M. pennsylvanicus) and the lack of recent specimens of Franklin's ground squirrel (Spermophilus franklinii) corroborate the hypothesis that prairie habitats have declined much more so than wooded habitats in the Chicago region. Based on ex- tinction models using museum records, it is probable that S. franklinii is already locally extirpated. Regression analysis suggests the white-footed mouse will be the only local Peromyscus in 0-140 years.
Deer mice, Peromyscus maniculatus, are found on all eight California Channel Islands and are classified as separate subspecies on each island. Distinct mitochondrial DNA haplotypes, identified by restriction enzyme analysis, were found in island deer mice, and on five of the eight islands deer mice have unique haplotypes, suggesting genetic isolation and independent evolution of several island subspecies. Founder effects on mtDNA diversity in island populations relative to mainland populations are evident. The connec-tivity of the deer mouse populations on East, Middle, and West Anacapa Islands (P. m. anacapae) was assessed using sequence data from the mitochondrial cytochrome c oxidase subunit II gene (COII). A common haplotype was found on all three Anacapa Islets, although Middle and East Anacapa each had an additional unique haplotype. This suggests that deer mice on Anacapa are functioning as a metapopulation, with some gene flow or extinction/recolonization occurring among the islets. Discriminant function analysis of cranial and external morphological characters for three island sub-species, P. m. anacapae, P. m. santacruzae, and P. m. elusus, produced a high rate of correct classification, indicating strong morphological as well as genetic differentiation. The specimens used for the morphometric study were museum specimens collected at different times during the past century. A surprising result of the morphological analysis was that each subspecies had exhibited extremely rapid change in several characters over this time period.
We perform a meta-analysis on morphological data from four island rodent populations exhibiting microevolution (>100 years). Data consisting of incidences of skeletal variants, cranial, and external measurements are from house mice (Mus musculus) on one Welsh and one Scottish island, black rats (Rattus rattus) on two Galapagos islands, and deer mice (Peromyscus maniculatus) on three California Channel islands. We report extremely high rates of microevolution for many traits; 60% of all mensural traits measured changed at a rate of 600 d or greater (max. 2682 d). The proportion of all mensural traits evolving at 600–800 d (23%) was idiosyncratic and departed from an expected negative exponential distribution. We argue that selection, rather than founder events, is largely responsible for the substantial shifts in morphology seen among insular rodents. Examining individual traits, there is a trend towards the nose becoming longer and wider, while the skull becomes shallower, shown by both rats and mice on five different islands. We found a significant correlation between island size and degree of skeletal variant evolution and between island distance from the mainland (or nearest island) and degree of cranial and external character evolution. Thus, microevolution of rodents is greater on smaller and more remote islands.
DnaSP is a software package for the analysis of DNA polymorphism data. Present version introduces several new modules and
features which, among other options allow: (1) handling big data sets (∼5 Mb per sequence); (2) conducting a large number
of coalescent-based tests by Monte Carlo computer simulations; (3) extensive analyses of the genetic differentiation and gene
flow among populations; (4) analysing the evolutionary pattern of preferred and unpreferred codons; (5) generating graphical
outputs for an easy visualization of results.
Availability: The software package, including complete documentation and examples, is freely available to academic users from: http://www.ub.es/dnasp
Expansions of population size leave characteristic signatures in mitochondrial "mismatch distributions." Consequently, these distributions can inform us about the history of changes in population size. Here, I study a simple model of population history that assumes that, t generations before the present, a population grows (or shrinks) suddenly from female size N0 to female size N1 . Although this model is simple, it often provides an accurate description of data generated by complex population histories. I develop statistical methods that estimate θ0 = 2uN0 , θ1 = 2uN1 , and τ = 2ut (where u is the mutation rate), and place a confidence region around these estimates. These estimators are well behaved, and insensitive to simplifying assumptions. Finally, I apply these methods to published mitochondrial data, and infer that a major expansion of the human population occurred during the late Pleistocene.
Deer mice, Peromyscus maniculatus, collected over 90 years from three California Channel Islands, were examined for evidence of morphological change. Rapid morphological change has occurred in the endemic subspecies from Santa Barbara (P. m. elusus), Anacapa (P. m. anacapae), and Santa Cruz Island (P. m. santacruzae). Data were divided into two temporal classes, 1897-1941 and 1955-1988. Of the 16 morphological characters measured, between five and 10 measures changed significantly (P ⩽ 0.05) with temporal class in each subspecies, and multivariate test statistics were significant (P ⩽ 0.05) for all three subspecies. For each subspecies, depth of braincase, total length, tail length, and hind foot length became smaller over time, except depth of braincase, which became larger in P. m. elusus. The rates of change dramatically exceed those estimated from paleontological records and are even higher than those reported in some experimental selection studies. Temporal change in two characters exceeds differentiation between subspecies. Although changing, each subspecies remained well differentiated, and incorporation of temporal change allowed correct classification of most specimens. Unlike nearly all previous reports of rapid evolution, the changes in these populations were not associated with a founder events or recent introductions. This study demonstrates that rapid phenotypic change can occur in long-established natural populations and temporal stability of morphological characters in such populations, even over short evolutionary time periods, cannot be assumed.
Episodes of population growth and decline leave characteristic signatures in the distribution of nucleotide (or restriction) site differences between pairs of individuals. These signatures appear in histograms showing the relative frequencies of pairs of individuals who differ by i sites, where i = 0, 1, .... In this distribution an episode of growth generates a wave that travels to the right, traversing 1 unit of the horizontal axis in each 1/2u generations, where u is the mutation rate. The smaller the initial population, the steeper will be the leading face of the wave. The larger the increase in population size, the smaller will be the distribution's vertical intercept. The implications of continued exponential growth are indistinguishable from those of a sudden burst of population growth Bottlenecks in population size also generate waves similar to those produced by a sudden expansion, but with elevated uppertail probabilities. Reductions in population size initially generate L-shaped distributions with high probability of identity, but these converge rapidly to a new equilibrium. In equilibrium populations the theoretical curves are free of waves. However, computer simulations of such populations generate empirical distributions with many peaks and little resemblance to the theory. On the other hand, agreement is better in the transient (nonequilibrium) case, where simulated empirical distributions typically exhibit waves very similar to those predicted by theory. Thus, waves in empirical distributions may be rich in information about the history of population dynamics.
Deer mice, Peromyscus maniculatus, collected over 90 years from three California Channel Islands, were examined for evidence of morphological change. Rapid morphological change has occurred in the endemic subspecies from Santa Barbara (P. m. elusus), Anacapa (P. m. anacapae), and Santa Cruz Island (P. m. santacruzae). Data were divided into two temporal classes, 1897-1941 and 1955-1988. Of the 16 morphological characters measured, between five and 10 measures changed significantly (P ≤ 0.05) with temporal class in each subspecies, and multivariate test statistics were significant (P ≤ 0.05) for all three subspecies. For each subspecies, depth of braincase, total length, tail length, and hind foot length became smaller over time, except depth of braincase, which became larger in P. m. elusus. The rates of change dramatically exceed those estimated from paleontological records and are even higher than those reported in some experimental selection studies. Temporal change in two characters exceeds differentiation between subspecies. Although changing, each subspecies remained well differentiated, and incorporation of temporal change allowed correct classification of most specimens. Unlike nearly all previous reports of rapid evolution, the changes in these populations were not associated with a founder events or recent introductions. This study demonstrates that rapid phenotypic change can occur in long-established natural populations and temporal stability of morphological characters in such populations, even over short evolutionary time periods, cannot be assumed.
The tendency for island populations to differ in body size from their mainland relatives has been well documented, but the mechanisms for these size changes remain speculative. Explanations have typically been based on ecological interactions that directly favor either an increase or decrease in body size. While it is clear that direct ecological interactions can influence body size, life history shifts present an alternative explanation for observed insular size trends across phylogenetic groups and trophic levels. Here I describe how decreased resource availability and reduced predation pressure, the same selective forces invoked by previous hypotheses, can operate to produce body size changes via the evolution of life history traits. This mechanism is more generally applicable than previous explanations and is consistent with much of the available data.
We evaluate methods for measuring and specifying rates of microevolution in the wild, with particular regard to studies of contemporary, often deemed "rapid," evolution. A considerable amount of ambiguity and inconsistency persists within the field, and we provide a number of suggestions that should improve study design, inference, and clarity of presentation. (1) Some studies measure change over time within a population (allochronic) and others measure the difference between two populations that had a common ancestor in the past (synchronic). Allochronic studies can be used to estimate rates of "evolution," whereas synchronic studies more appropriately estimate rates of "divergence." Rates of divergence may range from a small fraction to many times the actual evolutionary rates in the component populations. (2) Some studies measure change using individuals captured from the wild, whereas others measure differences after rearing in a common environment. The first type of study can be used to specify "phenotypic" rates and the later "genetic" rates. (3) The most commonly used evolutionary rate metric, the darwin, has a number of theoretical shortcomings. Studies of microevolution would benefit from specifying rates in standard deviations per generation, the haldane. (4) Evolutionary rates are typically specified without an indication of their precision. Readily available methods for specifying confidence intervals and statistical significance (regression, bootstrapping, randomization) should be implemented. (5) Microevolutionists should strive to accumulate time series, which can reveal temporal shifts in the rate of evolution and can be used to identify evolutionary patterns. (6) Evolutionary rates provide a convenient way to compare the tempo of evolution across studies, traits, taxa, and time scales, but such comparisons are subject to varying degrees of confidence. Comparisons across different time scales are particularly tenuous. (7) A number of multivariate rate measures exist, but considerable theoretical development is required before their utility can be determined. We encourage the continued investigation of evolutionary rates because the information they provide is relevant to a wide range of theoretical and practical issues.
Populations of animals and plants often undergo conspicuous ecological
changes when subjected to climatic extremes. Evolutionary changes may
accompany them but are less easily detected. We show that Darwin's
finches on a Galapagos island underwent two evolutionary changes after a
severe El Nino event caused changes in their food supply. Small beak
sizes were selectively favoured in one granivorous species when large
seeds became scarce. The effects of selection were transmitted to the
next generation as a result of high trait heritabilities. Hybridization
between this species and two others resulted in gene exchange, but only
after the El Nino when hybrid fitness was much enhanced under the
altered feeding conditions. These observations imply that if global
warming increases the frequency or severity of El Nino events on the
Galapagos, microevolutionary changes in animal and plant populations are
to be anticipated.
Morphological relationship among sympatric animal species have often been seen as indirect evidence for competition. Many early ecomorphological studies revealed patterns that were taken as indicating character displacement and character release, driven by competition or lack thereof. These patterns may result from a coevolutionary morphological response or from species sorting according to size. Thus, the relationship between morphology and competition may be crucial for understanding both the morphological evolution of animals and the role of competition in structuring communities. Some earlier research perceived as indicating morphological relationships conditioned by interaction of species was conducted on mammals, particularly carnivores. Subsequent criticism in the ecological literature demonstrated that many of the perceived patterns could not be statistically confirmed, thus calling into question this line of evidence for competition. More recent ecological literature relies on strong statistical analyses and careful consideration both of guild composition and of which morphological traits should be examined. This literature, resting largely on mammals, includes several cases that suggest a coevolutionary morphological response to interspecific competition. These studies have focused on the thropic apparatus directly related to food procurement by mammals — the teeth. Island mammals often show striking morphological patterns, some of which have been interpreted as resulting from release from competition with mainland species that have not reached islands. However, few of these patterns were critically evaluated to demonstrate their support for the hypothesis of character release. Despite several decades of interest and research, many questions regarding competitively induced morphological patterns remain unresolved and require further research. Mammals are especially promising subjects for such researh.
Conservation of the endangered red wolf (Canis rufus) bas become a controversial issue because its genetic and morphological composition has been altered by hybridization with coyotes (C. latrans) and possibly gray wolves (C. lupus) making its evolutionary origins difficult to ascertain. The evolutionary hypothesis based on morphological data is that the red wolf had an Early Pleistocene origin and was the predecessor of both modern coyotes and gray wolves. After 1940 red wolves hybridized with coyotes as the species vanished from the wild. In contrast to this ancient origin-recent introgression hypothesis, molecular data are more consistent with an origin through hybridization between gray wolves and coyotes. Interspecific hybridization may have occurred repeatedly over time prior to European settlement in the southcentral United States or may have been induced recently by anthropogenic changes. We review recent molecular evidence and present new results from the analysis of mitochondrial and nuclear DNA markers in Pre-1940 populations of red wolves. Our results are inconsistent with an ancient origin of the red wolf and support the hybridization model. We discuss possible hybridization scenarios and reasons for the red wolf reintroduction program to be concerned with the effects of genetic introgression from coyotes.
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From the Publisher:
Increasingly, researchers need to perform multivariate statistical analyses on their data. Unfortunately, a lack of mathematical training prevents many from taking advantage of these advanced techniques, in part, because books focus on the theory and neglect explaining how to perform and interpret multivariate analyses on real-life data. For years, Afifi and Clark's Computer-Aided Multivariate Analysis has been a welcome exception, helping researchers choose the appropriate analyses for their data, carry them out and interpret the results. Only a limited knowledge of statistics is assumed and geometrical and graphical explanations are used to explain what the analyses do. However the basic model is always given and assumptions are discussed. In this edition the computer emphasis is enhanced by the inclusion of three additional statistical packages written for the personal computer. The authors also discuss data entry, database management, data screening, data transformations, as well as multivariate data analysis. This third edition contains a new chapter on log-linear analysis of multi-way frequency tables. The new edition will be useful to professionals, researchers and students in a wide range of fields ranging from psychology, sociology and physical sciences to public health and biomedical science.
1. Data from 14 confined populations living under natural conditions (mainly on small islands) and from a few laboratory populations have been used.
2. Several differences between a typical, confined rodent population (i.e. living under natural conditions in a well isolated, homogeneous and relatively small area) and an open one have been determined.
3. Island populations are characterized by:
( a ) Attainment and maintenance of high densities not observed at all, or recorded only periodically, in open populations of comparable species.
( b ) Stability of population numbers, expressed either by very slight fluctuations or by a very regular cycle with only small differences between peaks of consecutive years.
(c) Lack of emigration resulting from any or all of the barriers surrounding the confined population, from homogeneity of the habitat enclosed by these barriers, or from a lower tendency to dispersal of individuals forming such populations.
( d ) Decreased reproduction.
(e) Low losses of independent individuals.
(f) Mortality of sucklings changing with the population density.
( g ) An age structure that is probably more differentiated and more regularly changing in an annual and long‐term cycle.
( h ) Different spatial organization based on smaller home ranges, that are differently arranged in relation to one another from those in open populations; the arrangement of home ranges allows the population to squeeze in a greater number of individuals with possibly the lowest number of interactions between individuals.
4. In confined populations there must be different mechanisms for the regulation of numbers from those in open populations: (I) in the latter the regulation occurs by the outflow of the surplus of independent individuals, i.e. through the dispersal and high mortality of migrants; (2) in confined populations the inflow of independent individuals is regulated by controlled reproduction and early mortality of offspring. Both mechanisms are induced by social pressure but in the second case (regulation of inflow) a much stronger social organization is indispensable Only those species that are capable of the formation of such an organization can survive as confined populations.
5. Knowledge of phenomena occurring in confined populations is useful for predicting the fate of populations of different species which become isolated as a result of human activity in transforming and subdividing the natural environment.
Microsatellite analysis was applied to scale samples of Atlantic salmon collected up to 60 years ago. Samples from the 1930s, from a now endangered Danish population, were compared with recent samples (1989), to test if the present population consists of descendants from the original one. Allele frequencies had changed over time, but individuals from the two samples caught about 60 years apart clustered together when compared with the closest neighbouring population and another reference population. However, fewer alleles were detected in the recent sample from the endangered population, most likely due to a population bottleneck or sampling artefacts.
Island populations are of interest for their differentiation as well as their species diversity; some of the earliest biological interest in islands was concerned with the number of ‘endemics’ thereon. There is dispute about the long-term evolutionary importance of island forms, but they are rich sources of data for studying the under-exploited interface of genetics, ecology and physiology. Differentiation of island populations may arise from genetic change after isolation, or from the chance collection of alleles carried by the colonizing group itself. The general reduction of genetic variance in island populations compared to continental forms of the same species suggests that founder events have played a major role in the formation of most island forms. However, there is ample evidence of adaptation in island populations despite this lower variation; this is relevant when using island biology as a base for the deriving of rules for genetic conservation.
Fluctuating asymmetry, or random deviations from bilateral symmetry, has been widely used as a measure of developmental stability. The relationship between fluctuating asymmetry (FA) and allozymic heterozygosity was evaluated using 18 natural populations of pocket gophers (Thomomys bottae). Heterozygosity in local populations of pocket gophers ranges over more than an order of magnitude (1.5—18.4%), making this burrowing rodent particularly apt for such studies. Two measures of FA in mensural skull characters were examined: absolute deviations between left and right sides and the variance of signed differences. After log transformations, levels of FA among individuals and populations were not related to size. Repeated-measures analyses of variance showed that FA was significant relative to measurement error, both across populations and within them. Asymmetries of different characters were uncorrelated, despite positive significant correlations among the characters themselves. FA levels varied only slightly among populations of gophers, and this variation was not significant for most characters. FA levels of populations were not correlated with allozymic heterozygosity, and analyses of variance in FA employing heterozygosity were not significant. Heterozygosity levels in these rodents appear more strongly related to aspects of population history (especially effective size and gene flow) than to developmental stability. Because so many genomic and environmental factors can affect morphological variation, caution is needed in interpreting correlations between genetic and phenetic variation.
In an earlier paper (Pergams & Nyberg 2001) we found that the proportion of the prairie deer mouse (Peromyscus maniculatus bairdii), among all local Peromyscus museum specimens collected in the Chicago region, had significantly declined over time. This proportion changed from about 50% before 1900 to <10% in the last 25 years. Based on this proportion a regression model predicted the local extinction of the prairie deer mouse in 2009. To evaluate that prediction, we estimated current deer mouse abundance by live trapping small mammals at 15 preserves in Cook and Lake counties, Illinois (USA) at which prairie deer mice had previously been caught or that still contained their preferred open habitat. In 1900 trap nights, 477 mammals were caught, including 251 white-footed mice (P. leucopus), but only one prairie deer mouse. The observed proportion of Peromyscus that were prairie deer mice, 0.4%, was even lower than the 4.5% predicted for 2000. Here we also introduce a simple, new community proportions model, which for any given geographic region compares the proportions of species recently caught with the proportions of species in museums. We compared proportions of seven species collected in Cook and Lake counties and examined by Hoffmeister (1989) with proportions of these species that we caught. Ten percent of the museum community was prairie deer mice, but only 0.2% of our catch was. The current local scarcity of the prairie deer mouse is consistent with the regression-based prediction of its eminent local extinction. More conservation attention should be paid to changes in relative abundance of once-common species.