Article

The exposition to urban habitat is not enough to cause developmental instability in the common wall lizards ( Podarcis muralis )

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Abstract

Developing trustworthy biomarkers is of primary importance in monitoring impacts of environmental stressors on biological systems. Recently, fluctuating asymmetry in morphological traits of the common wall lizard (Podarcis muralis) has been proposed as useful tools for assessing environmental disturbance in urban habitats. However, the experimental design used in previous studies lacked both site replication (only one urban area was sampled) and independent assessment of the physiological conditions of lizards. Hence, we replicated the analysis involving three large cities in Northern Italy and measured lizards' health conditions as assessed by blood sampling analyses. We found a weak statistical association between fluctuating asymmetry and urban habitat. No significant differences occurred for white blood cell concentration and heterophils-to-lymphocytes ratio, whereas parasite load was significantly lower in urban than natural populations. Finally, somewhat of the variability in fluctuating asymmetry correlated with one or more latent variables not directly observed, but still not related to the habitat. Contrary to previous studies, we concluded that fluctuating asymmetry cannot be regarded as a reliable measure of urban environmental stresses. Despite this, fluctuating asymmetry in the morphology of common wall lizards has a real potential for working as biomarkers, but we need to clarify first the developmental mechanisms, the true effectors of the stress, their interactions and their effects on individual fitness in order to solve the inconsistencies occurring among different studies.

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... In addition, living in the urban environment also reduced body condition and increased parasite loads in urban common wall lizards (Lazi c et al., 2017a). However, a recent study of urbanization effects on P. muralis where indicators of stress were FA of several morphological traits and leucocyte count, did not confirm these findings (Sacchi et al., 2018). Lack of studies and controversy in published results indicate more research is needed to provide wellgrounded conclusions regarding the impact of urbanization on common wall lizard populations. ...
... Phenodeviants are not uncommon in reptiles (Zakharov, 1989;Voipio, 1992). However, phenodeviants are usually neglected in studies of developmental instability in the lizard pileus (B ancilǎ et al., 2010;Lazi c et al., 2013Lazi c et al., , 2015Lazi c et al., , 2016Sacchi et al., 2018). Common practice is to exclude individuals with anomalies from studies of developmental instability of head, but in our case, the most striking result is that 52% individuals have pileus with postfrontal anomalies. ...
... Taking all results of our study into consideration, we cannot make an irrefutable conclusion that urbanization per se has the most negative effects on the common wall lizard populations (see Uro sevi c et al., 2015;Sacchi et al., 2018;but see Lazi c et al., 2015). It is important to emphasize that urbanization encompasses many factors (e.g. ...
Article
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Numerous studies of urban environment impact on wildlife imply urbanization can have both negative and positive effects. Phenotypic variation of pileus in the common wall lizard (Podarcis muralis) was analysed to determine whether urbanization levels can be associated with developmental instability induced by environmental stress. Pileus developmental pathways and instability in natural, suburban and urban populations were quantified by patterns of size and shape, fluctuating asymmetry (FA), modular organization and integration, allometric trajectories and frequency of phenodeviants. Our results show high asymmetry and modular structure of pileus with the high frequency of phenodeviants for natural, suburban and urban populations indicating elevated developmental instability in all three habitat types. However, some peculiarities were observed comparing habitats – the lowest level of FA and integration in urban populations and unexpectedly high level of FA and frequency of phenodeviants in the natural population. In addition, significant correlations between symmetric and asymmetric shape patterns, and presence of modular organization for all three habitat types suggest that genetic/environmental and developmental parcellation are somewhat aligned. Our results indicate that pileus morphology varies in a complex manner and future studies that link physiological, behavioural and morphological parameters to demographic parameters and fitness are necessary to fully understand how environmental stress affects developmental instability.
... FAhas already been used to describe influences of different environmental stressors in lacertid lizards, i.e. pollution and urbanization [9][10][11], population isolation [12,13], habitat fragmentation [14], incubation temperature [15], sexual selection [16], and locomotor performance [17,18]. These studies did not yield consistent results: some indicated that a stressful environment induces higher levels of FA, while others did not [9,14]. ...
... These studies did not yield consistent results: some indicated that a stressful environment induces higher levels of FA, while others did not [9,14]. In addition, a literature survey for studies involving lizards as a subject species showed that different methodological approaches were used for the estimation of FA levels; some authors compared FA levels between target groups using several morphological traits [9,11,13,15] while others used just one trait [14,[19][20][21]. As the FA indices can be calculated in many different ways [22], a literature survey showed the use of various FA indices in lizards, some were corrected or not for trait size, some were calculated for only one trait and others described multiple traits [11,13,19]. ...
... In addition, a literature survey for studies involving lizards as a subject species showed that different methodological approaches were used for the estimation of FA levels; some authors compared FA levels between target groups using several morphological traits [9,11,13,15] while others used just one trait [14,[19][20][21]. As the FA indices can be calculated in many different ways [22], a literature survey showed the use of various FA indices in lizards, some were corrected or not for trait size, some were calculated for only one trait and others described multiple traits [11,13,19]. ...
Article
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The use of fluctuating asymmetry (FA) as a measure of developmental instability and its relationship to stress and fitness is highly controversial. We examined whether the selection of different FA indices and traits influences the results of FA analysis. We chose four meristic traits and three FA indices (two single-trait and two multiple-trait indices) to assess FA levels in the common wall lizard (Podarcis muralis) from three different habitat types (urban, suburban and natural). Urbanization has already been linked to developmental instability in P. muralis. We therefore expected to detect different FA levels among the habitats. However, we also wanted to see whether we obtained the same patterns using different indices and traits. Our results showed that different traits can yield different FA patterns between habitats. The only statistically significant difference between habitats was detected for the FA2 index in femoral pores. The highest level of FA was detected in the urban population, while the lowest level was in the natural population. It is clear that caution must be exerted when deciding on which traits and indices are to be used for FA analysis. [Projects of the Serbian Ministry of Education, Science and Technological Development, Grant no. OI173043, Grant no. III43001]
... Fluctuating asymmetry has often been used as an indicator of stress in lizards [23,[37][38][39][40][71][72][73]. Lazić et al. [39,71] found in their research that FA is higher in populations exposed to urbanisation-induced stress, while Sacchi et al. [72] and Mirč et al. [40] found no association between the level of urbanisation and FA. ...
... Fluctuating asymmetry has often been used as an indicator of stress in lizards [23,[37][38][39][40][71][72][73]. Lazić et al. [39,71] found in their research that FA is higher in populations exposed to urbanisation-induced stress, while Sacchi et al. [72] and Mirč et al. [40] found no association between the level of urbanisation and FA. On the other hand, Vukov et al. [23] showed that the levels of FA may be lower in highly urbanised areas than in periurban and natural habitats. ...
Article
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Alpine habitats are exposed to increasing anthropogenic pressure and climate change. The negative impacts can lead to chronic stress that can affect the survival and reproductive success of individuals and even lead to population extinction. In this study, we analyse different morphological and ecological traits and indices of abiotic and biotic stressors (such as head size and shape, fluctuating asymmetry, body condition index, tail autotomy, and population abundance) in alpine and subalpine populations of two lacertid species (Zootoca vivipara and Lacerta agilis) from Serbia and North Macedonia. These lizards live under different conditions: allotopy/syntopy, different anthropogenic pressure, and different levels of habitat protection. We found differences between syntopic and allotopic populations in pileus size, body condition index (in both species), pileus shape, fluctuating asymmetry (in L. agilis), and abundance (in Z. vivipara). Differences between populations under anthropogenic pressure and populations without it were observed in pileus shape, body condition index (in both species), pileus size, fluctuating asymmetry, tail autotomy and abundance (in L. agilis). On the basis of our results, it is necessary to include other stress indicators in addition to fluctuating asymmetry to quickly observe and quantify the negative effects of threat factors and apply protective measures.
... For example, in carabid beetles, FA increased with urbanisation in species considered to be negatively affected by urbanisation, whereas such a relationship was not found in species that are more tolerant to urbanisation (Weller and Ganzhorn Year of capture ; however, in another study FA did not change along rural-urban gradients (Elek et al. 2014). Similarly, different studies in lizards have reported an increase in FA in response to urbanisation (Lazić et al. 2013), no changes in FA in response to urbanisation (Sacchi et al. 2018), and even a decrease in FA in response to urbanisation, the authors interpreting this last result as natural selection being stronger in urban populations and asymmetrical individuals being less likely to survive to adulthood ). ...
... Our data cannot possibly address these questions nor contribute to the controversial relationship between symmetry and fitness (Dongen 2006;Lens et al. 2002;Møller 1997). More detailed studies may provide more nuanced results (Sacchi et al. 2018). For example, FA was higher in bank voles (Myodes glareolus) in disturbed rural areas in the northern coast of France than in undisturbed rural areas (Marchand et al. 2003). ...
Article
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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.
... Otherwise, lizards are the most species-rich and widespread reptile group, comprising commonly studied genera both in temperate (e.g. Anolis, Podarcis; Avilés-Rodríguez & Kolbe, 2019; Sacchi et al., 2019) and tropical urban environments (e.g. Tropidurus, Intellagama; de Andrade, 2019; Littleford-Colquhoun et al., 2019). ...
Article
Global urban expansion has multiple impacts on biodiversity and ecosystem functioning. Still, urban centers may play an important role in the conservation of reptiles, an undersampled, megadiverse, and unevenly distributed group especially vulnerable to anthropogenic impacts. However, major gaps in research on urban ecology of reptiles and species responses to urbanisation persist, which may limit our capacity to guide suitable conservation policies. We conducted a global systematic literature review to evaluate biogeographic, taxonomic and ecological biases in urban ecology of reptiles, and ultimately to detect major gaps and steer future sampling efforts. Our database comprised 278 articles dealing with biological responses to urbanisation of 493 species across 45 countries and 12 biomes, comprising 658 cases between a given species and a specific biological response. Research on urban ecology of reptiles was geographically and taxonomically biased. Developed countries within temperate regions were better sampled, while developing tropical and megadiverse countries were mostly undersampled or neglected. Among reptile orders, Testudines and Crocodylia were proportionally more studied than Squamata. Across lower groups within Squamata, lizards were present in most studies and were the biological model most commonly used. Studies evaluating biological responses associated with landscape-level processes, behaviour, and/or population dynamics were prevalent, whereas conservation, human-reptile conflicts and wildlife management were the least considered topics. Our results show that research on urban ecology of reptiles is unevenly distributed across regions and lineages. Overcoming these major gaps is an important step toward the improvement of conservation of reptiles worldwide under the upcoming biodiversity loss scenario. Beyond spreading sampling effort across undersampled countries, taxa and research topics to meet conservation objectives, we recommend more multidisciplinary approaches to evaluate and compare the actual performance of reptiles in urban environments and to achieve the equilibrium between human well-being and species conservation.
... Results of other parasitological studies regarding reptiles in urban ecology context are inconsistent, showing confusing results. Elevated blood parasite load followed by reduced body condition index in females was observed in urban wall lizards (Podarcis muralis) (Lazić et al. 2017); however, Sacchi et al. (2018) documented reverse effect of urban areas on this species-urban wall lizards experienced weaker infections than individuals from suburban and natural areas. Similarly, brown anoles (Norops sagrei) experienced higher parasite load in urban areas than in natural habitats, while there were no differences in parasite load between crested anoles (Anolis cristatellus) from urban and natural habitats of Florida (Thawley et al. 2019). ...
Article
Land disturbances caused by urban development modify and create novel habitats with novel ecological pressures, which in turn may negatively affect remaining wildlife populations, e.g. by altering interspecific interactions. However, it is not clear whether these modified interactions, e.g. parasitism, affect urban wildlife negatively. This is especially true for reptiles, as even parasitism under natural conditions is understudied in this group. We have observed that up to 35% of grass snakes (Natrix natrix) are infected with the trematode Leptophallus nigrovenosus in urban areas of Kraków, while none of snakes sampled in nearby suburban and non-urban forests exhibited this infection. As this trematode typically inhabits the intestine, we suggest that its occurrence in the oral cavity may be a sign of very high infection rates. However, we did not detect any negative effects of observed infection on body size, mass and body condition of affected individuals. On the other hand, competition with other parasite species in suburban and non-urban habitats may be responsible for not detecting L. nigrovenosus in grass snakes from these sites. Nevertheless, interpretation of our findings is difficult, as knowledge on L. nigrovenosus biology is very limited. Our study underlines the necessity to fill the research gap in reptile parasitology.
... More detailed studies may provide more nuanced results (Sacchi et al. 2018). For example, FA was higher in bank voles (Myodes glareolus) in disturbed rural areas in the northern coast of France than in undisturbed rural areas (Marchand et al. 2003). ...
Preprint
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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.
... meristic features such as scales, femoral, and anal pores) bilateral traits that can be recorded easily in the field (Laia et al., 2015). Different studies, however, obtained antithetical results across species and environmental stressors, questioning the utility of FA as a reliable biomarker (Clarke, 1995(Clarke, , 1998Valkama and Kozlov, 2001;Dauwe et al., 2006, Sacchi et al., 2018. Indeed, the relationships between FA and environmental features could be feeble, not detectable due to small sample size, underestimated if only one trait is considered (Lens et al., 2002;Crnobrnja-Isailović et al., 2005), or masked by premature individual decease under high stress levels before adulthood (Polak et al., 2003). ...
Article
The extensive use of pesticides in agricultural environments produces drastic effects on wildlife, hence the need for less invasive indicators of environmental stress to monitoring the impact of agriculture treatments on biological systems. Fluctuating asymmetry (FA), as measure of developmental instability, has recently been proposed as reliable biomarker of populations stress due to environmental disturbance. We investigate femoral pores (FP) and dorsal head shape (HS) traits in populations of the Italian wall lizard inhabiting agricultural environments to examine whether different pesticide exposures (conventional, organic and control) can cause distinctive degree of FA. High-resolution photographs of FP and HS were taken in the field with a digital camera. The number of FP were counted twice on both sides and HS was analysed using geometric morphometrics with 25 landmarks and 12 semilandmarks. Individuals under conventional management showed higher levels of FA compared to control ones, and females exhibited higher FA levels than males for the FP. However, no significant difference was found for the HS trait. Our study provided evidence that FA may have a real potential as biomarker of population stress in wall lizards, highlighting the importance in the choice of the experimental design and the traits adopted for estimating DI.
... This process is associated with rising temperatures, increased air pollution, a decline of native vegetation with concomitant losses on biodiversity, changes in predatory pressures, privation of food resources, just to name a few (Gering and Blair, 1999;Ditchkoff et al., 2006;Murphy et al., 2016;Mackay et al., 2017). These stressful conditions could lead to a decrease in the fitness of individuals (Sacchi et al., 2018). Urban environments expose organisms to new selective pressures. ...
Article
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Urbanization causes the loss of large amounts of habitat and produces significant changes in environmental conditions with consequences in the individual's behavior, morphology, and physiology in natural populations. The urbanization can impact in the individual's development instability (DI) that may be measured with the fluctuating asymmetry (FA) level making it an environmental quality bioindicator. In addition, the FA of each trait should be interpreted considering the trait functional importance, morphogenesis and history of selection pressures. In this paper, we evaluated the impact of two decades of increasing urbanization levels over a population of the pampean scorpion Bothriurus bonariensis. We analyze the FA level in somatic and genital traits in adult individuals of both sexes, collected every ~ 10 years (1997, 2008, 2018). Interestingly, in this study the somatic traits (pedipalp chelae) would be under directional selection and are shaped throughout the individual's growth. In contrast, the genital traits (male's hemispermatophore) are involved in the sperm transfer process and could be under stabilizing selection. Also, hemispermatophores are affected for less time by environmental stressors since they are formed once the individual has reached sexual maturity. Our results showed a significant increase in the FA levels in somatic traits of males and females, according to the increase of urbanization along years. In contrast, genital traits showed no changes in the level of FA in females, and only a few male genital traits presented an increase in the FA level. This work shows evidence that the measured scorpion traits (under different selective pressures and morphogenesis) might present differences in their susceptibility to environmental stress. We discuss these results in a context of DI of individuals caused by urbanization. We support the idea that the level of FA can be useful as an index to evaluate the effects of environmental stress on invertebrate populations. Furthermore, our paper presents the scorpions as a good model that could be used as an indicator group for studying the impact of the anthropogenic disturbance factors on natural ecosystems.
Chapter
This chapter examines the crucial role of reptiles as environmental indicators, highlighting their importance in influencing current methods of environmental management. The fundamental principle of indicator species is the basis for understanding how reptiles function as tangible indicators of the overall health of ecosystems. They exhibit dynamic responses to changes in habitat, variations in climate, and disturbances caused by human activities. The incorporation of reptile monitoring into conservation efforts is increasingly recognized as a pragmatic and adaptable approach, providing significant contributions to the fields of biodiversity conservation, habitat management, and the alleviation of environmental risks. The discourse revolves around the examination of forthcoming challenges and opportunities, emphasizing the imperative for innovation, interdisciplinary collaboration, and community engagement. This paper emphasizes the necessity of adopting a comprehensive conservation approach, which emphasizes the importance of acknowledging and safeguarding the complicated interrelationships between reptiles and larger ecological processes. It examines the significant contribution of reptiles in serving as early indicators of ecosystem disruptions, facilitating informed habitat management strategies, and evaluating the effects of urbanization, pollution, and climate change. Upon the culmination of the exploration, a compelling appeal is made to advocate for the allocation of resources toward research, education, technological advancements, and global cooperation. These endeavors are crucial for fostering a sustainable future wherein reptiles assume a pivotal position in bolstering environmental resilience. Proposal for the integration of reptile monitoring findings into environmental management methods, with the aim to establishing a symbiotic relationship with the natural environment, and achieving equilibrium between human activities and the complex ecosystems represented by reptiles is also made.
Thesis
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Random and subtle deviations from bilateral symmetry (fluctuating asymmetry) have long been of interest to biologists who wish to study the susceptibility of organisms to changes in environmental quality. However, the reliability of FA as a biomarker has come under question due to inconsistent results in the literature. We conducted a meta-analysis of published literature to test the hypothesis that FA is a reliable biomarker of environmental stress in insects and identify possible sources of variation amongst studies. We expected studies to detect larger, positive magnitudes of effect on FA in lab populations due to the lack of confounding effects from other environmental factors compared to wild populations. Additionally, we predicted that studies that used geometric morphometric approaches to FA in shape and size would be more sensitive to changes in environmental quality compared to linear and meristic measures and thus show larger effects on FA. We also expected anthropogenic stressors to generate significantly larger effects on FA compared to naturally occurring stressors due to the organisms’ inability to buffer developmental pathways against a novel stressor. Finally, we predicted comparatively larger magnitudes of effect in studies that verified the environmental factor acting on the organism was a stressor by detecting negative effects on fitness-related traits. Overall, we found that FA is a sensitive biomarker of environmental stress. Environmental stressors explained 36% of the variation of effect on FA across studies. Studies that demonstrated a negative effect of the stressor on fitness-related traits showed significantly larger, positive magnitudes of effect on FA compared to studies that did not detect an effect from the environmental stressor. Additionally, studies conducted under laboratory conditions detected significantly larger, effects on FA compared to field-based studies. The kind of trait measured and the novelty of the stressor did not significantly account for differences amongst studies. Thus, the use of FA as a biomarker of environmental stress is a legitimate tool particularly when studies verify the biological relevance of stressors for the study organism.
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We analysed the relationship between incubation regime and fluctuating asymmetry in a cohort of juvenile lizards (Oligosoma suteri) incubated under laboratory conditions. We found no relationship between incubation temperature or water potential and the level of asymmetry in two cranial traits, although previous research showed profound effects of incubation temperature on gross morphology and hatching success. Our results suggest that fluctuating asymmetry is not a reliable indicator of developmental stress in this species.
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The present study reports the morphology of leukocytes of 12 European lacertid lizards (Podarcis sicula, P. tiliguerta, P. melisellensis, P. bocagei, P. muralis, Algyroides nigropunctatus, Lacerta viridis, L. bilineata, L. trilineata, L. oxycephala, Timon lepidus, and Zootoca vivipara) stained using May–Grünwald/Giemsa method. The morphology of white blood cells was very similar among species, suggesting a relative morphological uniformity within the lacertid lizards. For six species (i.e. P. sicula, P. tiliguerta, P. melisellensis, P. bocagei, P. muralis, and A. nigropunctatus), we determined the leukocyte differential counts, which may be considered representative of the normal values of the corresponding populations. These results may be useful either in clinical investigation to detect pathologies in wild individuals, as in management and conservation projects to assess the general health conditions of natural wild lizard populations.
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As anthropogenic stress increasingly affects the viability of natural populations of animals and plants, conservation ecologists are challenged to identify vulnerable populations before their demographic and/or genetic properties become irreversibly affected. Since traditional biomarkers of anthropogenic stress are often cumbersome to measure, and populations may thus go extinct before appropriate data can be obtained, there is a growing interest in individual-based markers that do not require repeated captures, are relatively easy to measure, and allow mitigating action one step ahead. One such marker, left-right asymmetry in bilateral symmetrical traits (“fluctuating asymmetry”, FA) has become an established bioassay of the quality and health of individuals and populations in evolutionary-ecological studies. However, the lack of a theoretical framework that predicts under which ecological conditions relationships between FA, stress and fitness can be expected, continues to hamper the use of FA in applied conservation. Here, we briefly review the concept, measurement and analysis of FA, and appraise its expediency in a selection of 21 avian studies covering environmental or genetic stress commonly encountered in conservation biology. The majority of studies met the basic statistical requirements of FA analysis, and two-thirds reported significant, positive relationships with environmental or genetic stress, although with substantial variation among traits, stresses, ages and sexes. In most cases, the observed heterogeneity in relationships with FA could be explained by taking into account both methodological and conceptual issues. Effect sizes ranged from very small (0.02) to very large (0.76), with a weighted average of 0.30, indicating that on average 9% of variance in the variable of interest was explained by FA. Given the intrinsic difficulties associated with FA analysis, conservation ecologists are advised to combine information from FA with that of other individual-based biomarkers, such as the study of growth-bar dimensions on developing feathers.
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With human activities increasingly impacting natural resources in relatively remote locations, there is a need for simple and efficient methods to explore the ecological consequences of these activities. Little is understood about the influences of off-highway vehicle (OHV) use on wildlife populations. We examined the effect of OHV activity on developmental instability in a phrynosomatid lizard (i.e., western fence lizard [Sceloporus occidentalis]) in the western Great Basin, USA. We measured fluctuating asymmetry (FA) of bilateral head-scale patterns in populations of lizards at 3 OHV and 3 non-OHV sites. Fluctuating asymmetry was higher at OHV sites relative to non-OHV sites, supporting the idea that OHV activity can stress wildlife populations. We found FA to be a good tool for uncovering responses to stress in natural populations, and we recommend exploring FA as a means of uncovering developmental instability in other systems that merit conservation interest.
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Female preference for dominant males is widespread and it is generally assumed that success in male-male competition reflects high quality. However, male dominance is not always attractive to females. Alternatively, relatively symmetric individuals may experience fitness advantages, but it remains to be determined whether males with more symmetrical secondary sexual traits experience advantages in both intra- and intersexual selection. We analysed the factors that determine dominance status in males of the lizard Lacerta monticola, and their relationship to female mate preference, estimated by the attractiveness of males' scents to females. Sexually dimorphic traits of this lizard (head size and femoral pores) appear to be advanced by different selection pressures. Males with relatively higher heads, which give them advantage in intrasexual contests, were more dominant. However, head size was unimportant to females, which preferred to be in areas marked by relatively heavier males, but also by males more symmetric in their counts of left and right femoral pores. Chemicals arising from the femoral pores and other glands might honestly indicate quality (i.e. related to the symmetry levels) of a male to females and may result from intersexual selection. Females may use this information because the only benefit of mate choice to female lizards may be genetic quality. Chemical signals may be more reliable and have a greater importance in sexual selection processes of lizards than has previously been considered.
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Wildlife-human interactions are increasing in prevalence as urban sprawl continues to encroach into rural areas. Once considered to be unsuitable habitat for most wildlife species, urban/suburban areas now host an array of wildlife populations, many of which were previously restricted to rural or pristine habitats. The presence of some wildlife species in close proximity to dense human populations can create conflict, forcing resource managers to address issues relating to urban wildlife. However, evidence suggests that wildlife residing in urban areas may not exhibit the same life history traits as their rural counterparts because of adaptation to human-induced stresses. This creates difficulty for biologists or managers that must address problems associated with urban wildlife. Population control or mitigation efforts aimed at urban wildlife require detailed knowledge of the habits of wildlife populations in urban areas. This paper describes the history of wildlife in urban areas, provides examples of wildlife populations that have modified their behavior as an adaptation to urban stresses, and discusses the challenges that resource managers face when dealing with urban wildlife.
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Fear lives among Everest’s mighty ice-fluted faces and howls across its razor-sharp crags. Gnawing at reason and enslaving minds, it has killed many and defeated countless others. But in 1953, Edmund Hillary and Tenzing Norgay stared into its dark eye and did not waver. On May 29, they pushed spent bodies and aching lungs past the achievable to pursue the impossible. At a terminal altitude of 29,028 feet, they stood triumphant atop the highest peak in the world. With nimble words and a straightforward style, New Zealand mountaineering legend Hillary recollects the bravery and frustration, the agony and glory that marked his Everest odyssey. From the 1951 expedition that led to the discovery of the Southern Route, through the grueling Himalayan training of 1952, and on to the successful 1953 expedition led by Colonel John Hunt, Hillary conveys in precise language the mountain’s unforgiving conditions. In explicit detail he recalls an Everest where chaotic icefalls force costly detours, unstable snow ledges promise to avalanche at the slightest misstep, and brutal weather shifts from pulse-stopping cold to fiendish heat in mere minutes. In defiance of these torturous conditions, Hillary remains enthusiastic and never hesitates in his quest for the summit. Despite the enormity of his and Norgay’s achievement, he regards himself, Norgay, and the other members of his expedition as hardworking men, not heroes. And while he never would have reached the top without practiced skill and technical competence, his thrilling memoir speaks first to his admiration of the human drive to explore, to understand, to risk, and to conquer.
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Although fluctuating asymmetry has become popular as a measure of developmental instability, few studies have examined its developmental basis. We propose an approach to investigate the role of development for morphological asymmetry by means of morphometric methods. Our approach combines geometric morphometrics with the two-way ANOVA customary for conventional analyses of fluctuating asymmetry and can discover localized features of shape variation by examining the patterns of covariance among landmarks. This approach extends the notion of form used in studies of fluctuating asymmetry from collections of distances between morphological landmarks to an explicitly geometric concept of shape characterized by the configuration of landmarks. We demonstrate this approach with a study of asymmetry in the wings of tsetse flies (Glossina palpalis gambiensis). The analysis revealed significant fluctuating and directional asymmetry for shape as well as ample shape variation among individuals and between the offspring of young and old females. The morphological landmarks differed markedly in their degree of variability but multivariate patterns of landmark covariation identified by principal component analysis were generally similar between fluctuating asymmetry (within-individual variability) and variation among individuals. Therefore there is no evidence that special developmental processes control fluctuating asymmetry. We relate some of the morphometric patterns to processes known to be involved in the development of fly wings.
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Prey–predator interactions are plastic behaviours shown by both players, which constantly modify their decisions depending on physiological conditions and ecological context. We investigated whether the behavioural response to repeated simulated predatory attacks varied between adult males of the common wall lizard, Podarcis muralis, inhabiting environments characterized by different degrees of human presence. Our aim was to detect possible effects of urbanization on antipredator responses, in terms of activity, time spent hidden in refuges and habituation. Moreover, since this lizard species exhibits intrapopulation colour polymorphism, we looked for the occurrence of possible correlations between antipredator strategy and individual ventral coloration. We found that urban lizards spent less time in their refuge after predatory attacks and decreased successive hiding times faster than rural lizards, suggesting different wariness towards a potential predator. Irrespective of population, yellow lizards gradually spent less time in the refuge before appearing and emerging outside than the other two morphs. Conversely, red lizards showed progressively longer appearance and emergence times after successive tests, suggesting a growing sensitization to the potential threat of a predatory attack. In conclusion, our study showed the occurrence of different levels of behavioural plasticity in common wall lizard's antipredator response: the population level, depending on ecological context, here different degrees of exposure to human disturbance, and the individual level, which suggests the occurrence of morph-specific antipredator strategies. Thus, using a lizard species as a model, we shed light on two key points of evolutionary ecology concerning both the antipredator response and the factors driving the maintenance of intraspecific polymorphism.
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Tools for performing model selection and model averaging. Automated model selection through subsetting the maximum model, with optional constraints for model inclusion. Model parameter and prediction averaging based on model weights derived from information criteria (AICc and alike) or custom model weighting schemes. [Please do not request the full text - it is an R package. The up-to-date manual is available from CRAN].
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Lizards required 2 yr to reach sexual maturity. An average of 2 clutches are produced per breeding season (April-July). Clutch size decreases with time. Some older females may produce a 3rd clutch in late July. Clutch size is strongly correlated with female body size. Population size showed little variation throughout this study. Average absolute density (excluding hatchlings) was 531/ha. The 1-yr-old cohort represented between 66-71% of the population. Maximum longevity is c5 yr. -from Authors
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We performed an analysis of fluctuating asymmetry (FA) on samples of lizards from a hybrid zone between fission 5 (F5) and multiple fission (FM2) chromosome races of the Sceloporus grammicus complex in central Mexico. Defining the zone are three diagnostic chromosome markers that demonstrate sharp concordant changes from one parental race to the other over a geographic distance of about 1 km. These chromosome markers allowed five classes of genotypes to be designated: parental F5, parental FM2, F1 hybrid, F1 x F5 backcross, and F1 x FM2 backcross. We counted seven bilateral meristic characters on each individual lizard (n = 427). These characters were canthal scales, parietal border scales, post-rostral scales, nasal border scales, circumorbital scales, pes toe lamellae of fourth digit, and manus toe lamellae of fourth digit. We tested the prediction that 'hybrid' individuals (F1, F1 x F5 backcross, F1 x FM2 backcross) should show lower levels of developmental stability and thus higher levels of FA than parental individuals. Hybrids demonstrated significantly lower FA levels than parental classes in most pairwise tests for canthal, parietal border, and post-rostral scale characters. Parentals demonstrated a significantly lower level of FA than hybrids for just one pairwise test (canthal scale). Thus, in general, these results do not support the hypothesis that hybrids should demonstrate lower levels of developmental stability and corresponding higher levels of FA.
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Urbanization - the anthropogenic conversion of natural ecosystems into human-dominated ecosystems - has occurred on global scales. The human-dominated landscape presents particular challenges to researchers because the effects of urbanization on ecological processes are not well understood. We investigated the influence of urbanization on predation by conducting an artificial nest experiment along an urban gradient of six sites ranging from natural to urbanized ecosystems. Previous hypotheses suggest that predation pressures in urban environments will either 1) increase because of the high abundance of exotic species which act as predators or 2) decrease due to the lack of natural predators. To determine relative predation pressures among sites along the urban gradient, we monitored the fates of 16 artificial avian nests at each of the six sites for a total of 96 nests in each year (1996, 1997). We analyzed the dependency of nest fate (depredated or undisturbed) on intensity of urbanization (sites along the urban gradient), nest height (ground, above-ground), and year using loglinear models. The frequency of nest predation was strongly dependent on site along the urban gradient, indicating that urbanization intensity was an important determinant of nest fate. Predation pressure exhibited an overall decline from natural to urban sites in both years, suggesting that urban environments have low predation pressures relative to natural areas. The predatory relaxation in urban environments may partially explain the greater abundance of some species in urban environments, particularly urban exploiters such as european starlings Sturnis vulgaris, house sparrows Passer domesticus, and rock doves Columba livia.
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In most cases, prey animals do not escape randomly, but toward a refuge such as a rock crevice, burrow, tree, or a patch of thick vegetation. Safer habitats where animals restrict most of their activity to avoid exposure to potential predators found in other places are often called refuges or refugia (e.g., Werner et al. 1983). That is not our meaning of refuge in this chapter. Here, a refuge refers to small portions of the habitat where a prey hides temporarily after escaping from a predator that has been detected or that has attacked the prey. By definition, a refuge is a physical structure or some part of a habitat where the predator cannot enter to follow and capture the prey, or is at least impeded from doing so. Therefore predation risk immediately decreases, sometimes to zero, when the prey enters a refuge and hides inside it. Numerous studies have shown that prey often respond to predator presence by increasing their use of refuges or safe microhabitats (Lima & Dill 1990; Sih et al. 1992). However, most prey animals do not spend their lives in the safety of a refuge (Sih 1997) because by staying in refuges prey often incur some fitness costs that should be minimized (e.g., the loss of time available for foraging; Godin & Sproul 1988; Koivula et al. 1995; Dill & Fraser 1997; Martín et al. 2003a; Blumstein & Pelletier 2005; or mate searching; Sih et al. 1990; Martín et al. 2003b; Reaney 2007). Unfavorable conditions in refuges (e.g., suboptimal temperatures or oxygen levels) might also entail physiological costs, such as hypothermia or hypoxia (Wolf & Kramer 1987; Martín & López 1999b; Polo et al. 2005). And, finally, refuges are often useful against some types of predators, but can expose of prey to other type of predators, which can cause a conflict in refuge use (Soluk 1993; Sih et al. 1998; Amo et al. 2005).
Article
Abstract We measured the level of fluctuating asymmetry (FA) in head shape, head scalation and femoral pores in two lizard species (Podarcis bocagei and Podarcis hispanica) from 13 islands and 15 mainland localities in the Ria de Arosa archipelago of north-western Spain. Given the recent geological history of the region, the degree of isolation to which lizard populations have been subjected can be ordered along a spatio-temporal gradient, yielding the following hypotheses to be tested: FA will be higher (1) in island populations than in mainland populations; (2) on remote islands than on islands close to the mainland; (3) on small islands than on large islands. Molecular genetic data suggest that P. hispanica is autochthonous in the Ria de Arosa, whereas P. bocagei is a more recent arrival. Therefore, we predict also (4) a higher level of FA in P. hispanica than in P. bocagei. Statistically significant results were obtained for head-shape asymmetry, supporting the second and the fourth hypotheses. With an overall meristic asymmetry index, none of the hypotheses were corroborated, whereas for certain independent meristic traits, the first, the third and the fourth hypotheses were partially supported. Both head shape and meristic traits constitute precise measures of FA, but FA is more convincingly expressed in head shape and in single meristic traits than in overall meristic traits asymmetry. We conclude that FA reflects population isolation and may be a good indicator of developmental instability. It seems worthwhile to test for FA in a landlocked system under environmental and genetic stress, for the purpose of conservation biological assessments.
Article
© 2008 The Authors. Journal compilation © 2008 British Ecological Society ... The use of leukocyte profiles to measure stress ... AK Davis1*, DL Maney2 and JC Maerz1 ... 1D.B. Warnell School of Forestry and Natural Resources, The University of Georgia, Athens, GA 30602, USA; ...
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The use of both linear and generalized linear mixed‐effects models ( LMM s and GLMM s) has become popular not only in social and medical sciences, but also in biological sciences, especially in the field of ecology and evolution. Information criteria, such as Akaike Information Criterion ( AIC ), are usually presented as model comparison tools for mixed‐effects models. The presentation of ‘variance explained’ ( R ² ) as a relevant summarizing statistic of mixed‐effects models, however, is rare, even though R ² is routinely reported for linear models ( LM s) and also generalized linear models ( GLM s). R ² has the extremely useful property of providing an absolute value for the goodness‐of‐fit of a model, which cannot be given by the information criteria. As a summary statistic that describes the amount of variance explained, R ² can also be a quantity of biological interest. One reason for the under‐appreciation of R ² for mixed‐effects models lies in the fact that R ² can be defined in a number of ways. Furthermore, most definitions of R ² for mixed‐effects have theoretical problems (e.g. decreased or negative R ² values in larger models) and/or their use is hindered by practical difficulties (e.g. implementation). Here, we make a case for the importance of reporting R ² for mixed‐effects models. We first provide the common definitions of R ² for LM s and GLM s and discuss the key problems associated with calculating R ² for mixed‐effects models. We then recommend a general and simple method for calculating two types of R ² (marginal and conditional R ² ) for both LMM s and GLMM s, which are less susceptible to common problems. This method is illustrated by examples and can be widely employed by researchers in any fields of research, regardless of software packages used for fitting mixed‐effects models. The proposed method has the potential to facilitate the presentation of R ² for a wide range of circumstances.
Article
In the region of First near Grindelwald (Swiss alps) alpine marmots Marmota marmota reacted differently to various forms of hiking tourism. The smallest reaction was recorded when hikers kept to trails. The reaction increased with cross-country hiking and was even greater when the main burrows of the animals were crossed. The severest reaction was seen in experiments with dogs on a long leash.It can be concluded that the predictability and potential threat (dogs) are decisive factors in the reactions of marmots to different forms of hiking.
Article
Prey often respond to predator presence by increasing their use of refuges. However, refuge use may have some costs such as lost opportunities for foraging, and also physiological costs, such as hypothermia. Many lizards escape from predators by fleeing into rock crevices, which because of shady and colder conditions decreases their body temperature below required optimal levels. By experimentally increasing the frequency of attacks by a simulated predator (human) toward a group of wall lizards, Podarcis muralis, we examined the hypothesis that lizards may respond to an increase in risk of predation with an increase in refuge use, but that this strategy entails costs to their body condition. At the end of the experimental period, experimental lizards increased thr time spent in a refuge after an attack (recovery time), but they had significantly lower relative body mass than control individuals. We suggest that an increase in the rime spent in refuges at unfavourable temperatures during the experiment led to a loss of time available for foraging and a diminution of the efficiency of physiological functions, which resulted in loss of mass.
Article
Prey often respond to predator presence by increasing their use of refuges. However, unfavorable thermal conditions in refuges might entail physiological costs for an ectothermic prey. Thus, the decision of when to come out from a refuge should be optimized by considering the expected fitness effects of diminution of predation risk with time, but also by considering the cost of the loss of time spent at optimal body temperature maximizing physiological functions. The model of Ydenberg and Dill describes the trade-off between risk and cost for a prey fleeing to a refuge. We present a special case of this model to predict how emergence time from the refuge in lizards or other ectotherms should vary as a function of risk of predation and thermal costs of refuge use. The analyses of the variation in emergence time from a refuge of Lacerta monticola lizards in the held under two different predation risk levels supported the predictions of the model. As predicted, time spent in the refuge tvas longer when the threat of the initial attack had been higher, and therefore the subsequent diminution of risk was slower, but only when lizards emerged at the same place where they hid. When initial body temperature was high, some lizards decreased emergence time by emerging from a different place. In addition, the effects of thermal costs were more relevant in the highrisk situation. Time spent in the refuge under high risk increased when thermal conditions of the refuge were more similar to thermal conditions outside (i.e., physiological costs of refuge use were lower). We conclude that optimization of refuge-use strategies might help lizards cope with changes in predation risk without incurring excessive physiological costs.
Article
We examined degree of between-sides difference in number of femoral pores (fluctuating asymmetry, FA) in Podarcis muralis populations, distributed on islands and in coastal area of Lake Skadar (Southern Montenegro). The aim of this study was to test sensitivity of fluctuating asymmetry of chosen trait to isolation effect in the absence of anthropogenic impacts. The results indicate that FA in the number of femoral pores do not vary significantly between insular populations of P. muralis. Generally, there is negative but non-significant correlation between island size and FA level. Also, overdominance hypothesis of enhanced developmental homeostasis at higher levels of heterozygosity was not confirmed in this study. The results support earlier conclusions obtained from electrophoretic studies, that analyzed insular populations from Lake Skadar archipelago still do not suffer deleterious effects as a result of isolation.
Article
Ultrasound imaging is a promising technique for studying the reproductive biology of reptiles, but it has yet to be validated for small lizards in field research. This study aimed both at assessing the reliability of ultrasound imaging in field research and the measurement of the breeding effort and timing of reproduction in the northern Italian female population of the common wall lizard, Podarcis muralis. To this end, we kept 22 gravid females in captivity in April and June 2010 and used ultrasonography to predict the number of eggs they laid. The following year, we applied the same technique to monitor the breeding performance of females in their natural habitat. We collected 119 females between March and June 2011 and used ultrasonography to evaluate clutch size and egg developmental stage. Our results showed that 20 out of 22 females (91%) laid the exact number of eggs predicted. The field research showed that the percentage of gravid females varied over the season, showing a clear bimodal pattern with two peaks in late April and late May. These peaks corresponded to the first and second clutch depositions, respectively. Furthermore, female common wall lizards reach sexual maturity at a body size of 50–51 mm snout–vent length, at around 2 years of age. Mean clutch size in our population ranged from 2 to 5.5 eggs, with an average of 3.6 eggs. There was a strong positive relationship between clutch and female size, which was only statistically significant in the first deposition. The female lizards in our study were smaller than those in French and central European populations, they reached maturity at 50.9 mm and they laid few eggs. In this paper, we discuss some potential explanations for such differences.
Article
The use of fluctuating asymmetry (FA) as a measure of developmental instability, and its relationship to stress and fitness, is highly controversial. Here, we present results from a preliminary study comparing levels of asymmetry in various characteristics between two island populations of the Italian Wall Lizard (Podarcis sicula), one of which was recently founded. We relate individual asymmetry to several measures of physiological performance. Levels of FA varied clearly among the traits studied. Repeatability of FA estimates was high for meristic traits but low for metric traits. Levels of FA were on average higher in the newly founded population. We found a significant decrease in exertion (time until exhaustion by continuously chasing) with increasing levels of fluctuating asymmetry (i.e., more symmetric individuals had a higher exertion). Speed of locomotion showed a positive trend with increasing FA. No relationship was found between individual levels of FA and bite force. These results suggest that FA estimates, based on the accurate measurement of several traits, may be useful in explaining differences in developmental stability and physiological performance at the individual and population level.
Article
Urbanization - the anthropogenic conversion of natural ecosystems into human-dominated ecosystems - has occurred on global scales. The human-dominated landscape presents particular challenges to researchers because the effects of urbanization on ecological processes are not well understood. We investigated the influence of urbanization on predation by conducting an artificial nest experiment along an urban gradient of six sites ranging from natural to urbanized ecosystems. Previous hypotheses suggest that predation pressures in urban environments will either 1) increase because of the high abundance of exotic species which act as predators or 2) decrease due to the lack of natural predators. To determine relative predation pressures among sites along the urban gradient, we monitored the fates of 16 artificial avian nests at each of the six sites for a total of 96 nests in each year (1996, 1997). We analyzed the dependency of nest fate (depredated or undisturbed) on intensity of urbanization (sites along the urban gradient), nest height (ground, above-ground), and year using loglinear models. The frequency of nest predation was strongly dependent on site along the urban gradient, indicating that urbanization intensity was an important determinant of nest fate. Predation pressure exhibited an overall decline from natural to urban sites in both years, suggesting that urban environments have low predation pressures relative to natural areas. The predatory relaxation in urban environments may partially explain the greater abundance of some species in urban environments, particularly urban exploiters such as european starlings Sturnis vulgaris. house sparrows Passer domesticus. and rock doves Columba livia.
Article
Trade-offs between reproduction and survival are important determinants of life-history characteristics of lizards. Organisms cannot increase the allocation of limited resources to reproduction without diverting a proportional amount of energy from another trait. Locomotor performance is an ecologically relevant trait that potentially influences survival by affecting the ability to escape from predators. Most studies have used female lizards as subjects because pregnancy is known to reduce their locomotor abilities, whereas little is known on costs of reproduction in males. In this study we suggest that in males of the lizard Lacerta monticola reproductive investment in morphological traits that confer dominance (i.e. head size) might lead to a low probability of survival by decreasing investment in other traits that affect locomotor performance (i.e. limb symmetry). We staged laboratory agonistic encounters between males and measured their morphology and burst speed on a race track to examine possible relationships between morphology, social dominance and locomotor capacity. Our results indicate that social dominance was positively related to relative head height, and that escape speed was negatively related to levels of fluctuating asymmetry in femur length, but also negatively related to relative head height. Males with greater relative head height also had more asymmetrical femurs, thus dominant males suffered a decrease in locomotor performance. Males with higher heads tend to dominate male–male interactions and hence may gain access to reproductive females, thus increasing their current reproduction success. However, this might occur at the expense of future survivorship mediated by a decrease in escape speed. Therefore, in male L. monticola there might be a trade-off between current reproductive success and survival. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002; 77, 201–209.
Article
The research investigating fluctuating asymmetry (FA), a phenotypic proxy of developmental instability, as a potential early-warning biomarker of anthropogenic stress like habitat fragmentation has produced controversial results. We examined the influence of habitat fragmentation at the landscape-scale, divided into habitat amount and configuration, on feather length FA in the Eurasian treecreeper (Certhia familiaris), an area-sensitive old-growth forest passerine breeding in boreal forests that are currently under intense management. Our study included one tail and wing feather, measured in both sexes of the 14-day-old nestlings and adults. Habitat amount was measured as the proportions of suitable forest habitats and open unsuitable areas, mean patch isolation and nesting patch size whereas habitat configuration was measured as mean patch density, size and shape and edge density. We found only weak sex- and age-related associations between feather length FA and habitat fragmentation that explained just 4.9% of variance in FA. Habitat loss was associated with higher FA in males only while the habitats with low degree of configuration tended to be related to lower FA in adults only. From the biomarker perspective, FA may not thus hold a great promise as a strong and general indicator of habitat fragmentation.
Article
The flight response of fallow deer (Dama dama) towards human observers was studied in an enclosed population using fixed transects. Groups took flight less often when in open habitats, in large group sizes and at high distances from the transect. Flight was also less common where human activity was higher. This effect was marked, probably because the study was carried out in an enclosure where disturbance was frequent, regular and predictable. We suggest that these results may indicate that the flight response of fallow deer depends on the level of security provided by their immediate environment and their habituation to human presence. In addition, we observed that female groups took flight more often than other group types, possibly due to differences in ecological strategy whereby protection of young is a high priority for females. One of the most striking features of our results was the high inter-individual variability in flight response. This emphasises the need for individual-based behavioural studies.
Article
A causal link between morphology and performance is a central tenet of ecomorphological analyses, but there are few detailed analyses of exactly how morphological variation within a hatchling cohort maps onto locomotor performance, and especially whether or not different tasks favour different morphologies (or vice versa). We measured morphological traits (including body length, mass, head size, limb proportions and fluctuating asymmetry [FA]) on a large sample of laboratory-incubated hatchling lizards (Amphibolurus muricatus, Agamidae), and used principal component analysis to reduce this data set to four major axes of variation (size, shape and two FA axes). Running speeds of each lizard were measured on raceways at four inclines, from level (0°) through to steep (45°). Unsurprisingly, steeper inclines reduced locomotor speeds. Absolute body size was the only morphological trait that was consistently related to sprinting performance, and the relationships were similar at each incline. Within-cohort variation in body shape and FA among this large sample was unrelated to locomotor speeds, thus challenging the common assumption of a causal link between these variables. The only exception was a weak trend for greater hind limb length to enhance locomotor performance more at steep inclines than at shallower angles. In general, our data suggest that different morphological traits do not differentially maximize locomotor performance up variable inclines. Overall, our data provide a cautionary note about the generality of causal connections between within-cohort morphological variation and locomotor performance under different environmental contexts.
Article
Sexual selection theory suggests that females may gain significant indirect fitness benefits from mating with males expressing good genes, particularly in animal species where the males provide no parental care. Whole-organism performance abilities have previously been shown to enhance both survival and reproductive success in a range of taxa, and females who mate with high-performance males might therefore gain significant indirect performance benefits. We tested the hypothesis that females associate preferentially with high-performance males in the green anole lizard Anolis carolinensis in laboratory trials using multivariate statistical techniques. Our results indicate that male performance abilities do not influence female mating preferences, either in isolation or as a combined suite of traits. Thus, any indirect performance benefits that a female might gain for her offspring are likely not a result of a female choice process.
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The response of an Australian arid-zone gecko community to sulphur dioxide and salt spray from a mine and industrial site was investigated from 1992 to 1995. Geckos were abundant and fecund at control sites in chenopod shrubland and annual capture rates were strongly influenced by minimum night temperatures. Capture rate and percentage of females gravid at sites exposed to high concentrations of air pollutants were significantly lower than at control sites. Discrepancies between control and impacted sites were greatest for the termite-specialist geckos Diplodactylus conspicillatus and Rhynchoedura ornata. An increase in capture rates and percentage of females gravid at sites close to the industrial site, followed a reduction in peak sulphur dioxide emissions. Geckos may be sensitive and useful bioindicators of the environmental impacts of some atmospheric pollutants.
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The theory that fluctuating asymmetry is sensitive to both environmental and genetic stress is gaining acceptance among evolutionary biologists. Most empirical work has focused on ornamental traits on the assumption that they are more susceptible to stress. In tegumentary coloration is a common ornament in nature, and frequently has a hormonal basis. Earlier studies in the lizard Psammodromus algirus indicate that testosterone induces the development of head nuptial coloration in large males and, at the same time, produces an increase of the ectoparasite load and higher mortality. Hence, the manipulation of testosterone levels may be a way to increase ornament expression and simultaneously create conditions that may make symmetrical development difficult. This positive covariation between character size and symmetry is opposite to that expected in theory for sexually selected traits, so the predicted elevation of asymmetry due to the treatment cannot be confounded by any intrinsic association between symmetry and character size. We firstly consider the effect that testosterone supplementation has on two variables that reflect the symmetry of bilateral throat nuptial coloration in large P. algirus males. Also, we examine whether ornament symmetry is positively associated with reproductive success, a prediction of theory of sexually selected symmetry. Testosterone treatment did not increase the fluctuating asymmetry of throat coloration. Size asymmetry increased with character size in individuals with a fragmented colour pattern, but changed suddenly to a highly symmetric pattern in individuals with non-fragmented coloration. Mirror asymmetry decreased steadily with character size. These results suggest that the development of coloration on both sides of the throat midline follows a random pattern. Asymmetry did not correlate with variables that estimated reproductive success, suggesting that asymmetry is not affected by physiological stress and that this trait is not a sexually selected signal in P. algirus.
Article
The process of species formation is often ignored in discussions on the conservation of biodiversity. Yet the clearance of vegetation may promote divergence among populations of a species through isolation, providing conditions for rapid genetic drift and novel selection pressures. Here, stepwise discriminant function analysis and fluctuating asymmetry are used to examine variation in morphology within and among non fragmented and recently fragmented populations of two species of gecko,Oedura reticulata andGehyra variegata. High reclassification error rates using discriminant function analysis, indicate that fragmentation has had no detectable effect on morphological differentiation among populations of either species. In contrast, remnant populations of both species exhibit higher mean levels of fluctuating asymmetry than do populations in undisturbed habitat. ForOedura reticulata, levels of fluctuating asymmetry are negatively correlated with the log of adult population size. These results suggest that the changes following habitat clearance have been severe enough to cause increased developmental instability in populations of both species but not detectable morphological divergence. Given the high rate of extirpation of gecko populations in the study region and the extreme vulnerability of the remaining populations, it is unlikely that species formation will be significant in maintaining reptile diversity in that region.