Article

Life cycle, reproductive patterns and their year-to-year variation in a field population of the wolf spider Pirata piraticus (Araneae, Lycosidae)

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Abstract

Patterns of growth, phenology and reproduction were studied in a field population of the wolf spider Pirata piraticus from November 1997 until October 1998 and in June 1999 to unravel the intrapopulation variation and co-variation of these traits. Individuals of P. piraticus overwinter as juveniles of different instars while adults were found from the end of April until September. Strong year to year variation in the age and size of overwintering juveniles was present, resulting in a corresponding difference in adult size in the subsequent breeding season. The main period of reproduction occurred from May until August with larger individuals breeding earlier in the season. The size at which adults breed was also significantly different in the successive years. Clutch mass (cocoon mass), clutch volume and fecundity are dependent on the size of the female according to a weakly negative allometric relationship. The differences in those reproductive traits between the succesive years are therefore proportionate to the differences in female size. This was in clear contrast to egg size, a life history trait that shows much less variation and appears to be independent of female size. Therefore, egg size was not significantly different between spring 1998 and spring 1999. There is, however, some variation in fecundity due to egg size and number independent of female size. When corrected for female size, females with larger eggs produce relatively fewer eggs indicating a trade-off between these two reproductive characters.

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... In this study, we measured levels of FA in six populations of the wolf spider Pirata piraticus (Clerck, 1757) that vary in degree of metal exposure. In a previous study, life history patterns indicative for low growth and/or low reproductive environments were observed in the most contaminated populations (Hendrickx et al., 2003a). This was reflected by a severe reduction in clutch mass and, hence, female fecundity. ...
... Populations SA, GS, GW and KR were all located on the banks of the river Schelde, a tidal river known to be severely polluted by heavy metals during the last century (Zwolsman et al., 1996). Two inland populations DV and MO showed lower levels of metal contamination (Hendrickx et al., 2003a). All spiders were kept individually and killed and stored in a freezer at )10 °C in the laboratory. ...
... Repeated measurements were taken several days apart. For the measurement of the life history traits clutch mass and egg size, we refer to Hendrickx et al. (2003a). ...
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Although developmental instability, measured as fluctuating asymmetry (FA), is expected to be positively related to stress and negatively to fitness, empirical evidence is often lacking or contradictory when patterns are compared at the population level. We demonstrate that two important properties of stressed populations may mask such relationships: (i) a stronger relationship between FA and fitness, resulting in stronger selection against low quality (i.e. developmental unstable) individuals and (ii) the evolution of adaptive responses to environmental stress. In an earlier study, we found female wolf spiders Pirata piraticus from metal exposed populations to be characterized by both reduced clutch masses and increased egg sizes, the latter indicating an adaptive response to stress. By studying the relationship between these two fitness related traits and levels of FA at individual level, we here show a significant negative correlation between FA and clutch mass in metal stressed populations but not in unstressed reference populations. As a result, levels of population FA may be biased downward under stressful conditions because of the selective removal of developmentally unstable (low quality) individuals. We further show that females that produced larger eggs in stressed populations exhibited lower individual FA levels. Such interaction between individual FA and fitness with stress may confound the effect of metal stress on FA, resulting in an absence of relationships between FA, fitness and stress at the population level.
... So far, the role of MTLPs in metal tolerance in terrestrial organisms has been studied in collembolans, nematods, isopods, gastropods, earthworms, Drosophila, birds and mammals (Dallinger et al., 2000; Znidarsic et al., 2005; Carpene et al., 2007; Hughes and Stürzenbaum, 2007; Vanparys et al., 2008; Janssens et al., 2009). However, less extensively studied invertebrates that play key ecological roles in ecosystems, such as spiders, have also been shown to persist in heavily metal-polluted habitats (Salo et al., 1991; Marczyk et al., 1993; Wilczek and Migula, 1996; Wilczek and Babczynska, 2000; Hendrickx et al., 2003). Nevertheless, the importance of the intrinsic functional characteristics of this species group to tolerate high levels of metal exposure remains poorly understood. ...
... Nevertheless, the importance of the intrinsic functional characteristics of this species group to tolerate high levels of metal exposure remains poorly understood. Spiders are macro-concentrators of metals due to their role as predator and polyphage (Dallinger and Rainbow, 1993; Marczyk et al., 1993; Maelfait and Hendrickx, 1998; Heikens et al., 2001; Hendrickx et al., 2003; Jung et al., 2008). Contrary to insects, which mainly excrete metals (Van Straalen et al., 1987; Janssen et al., 1991; Lindqvist, 1994), detoxification mechanisms in spiders are mainly based on storage in intracellular granules (Brown, 1982; Hopkin, 1989; Janssen et al., 1991; Kramarz, 2000; Wilczek and Babczynska, 2000). ...
... Lycosids are particularly suited to model physiological stress responses as they often reach high densities in severely polluted ecosystems (Wilczek and Babczynska, 2000; Wilczek et al., 2005; Jung et al., 2008). Earlier studies on two other lycosid spiders, Pardosa amentata (Kramarz, 2000) and Pirata piraticus (Hendrickx et al., 2003), showed linear increases in internal cadmium concentrations during experimental exposure and zero or very low bioelimination rates for Cd, Zn and lead (Pb). Due to their active hunting strategy and predation on Diplopoda, Collembola and Isopoda, that are known to store metals, Lycosids show significantly higher internal metal concentrations compared to other soil-dwelling invertebrates and other spider families inhabiting polluted habitats (Van Hook and Yates, 1975; Hunter et al., 1987; Larsen et al., 1994; Rabitsch, 1995; Maelfait, 1996; Köhler, 2002; Hendrickx et al., 2004; Wilczek et al., 2004; Jung et al., 2008). ...
Article
Both local adaptation and acclimation in tolerance mechanisms may allow populations to persist under metal pollution. However, both mechanisms are presumed to incur (energetic) costs and to trade-off with other life-history traits. To test this hypothesis, we exposed Pardosa saltans (Lycosidae) spiderlings originating from metal-polluted and unpolluted sites to a controlled cadmium (Cd) treatment, and compared contents of metal-binding metallothionein-like proteins (MTLPs), internal metal concentrations, and individual survival and growth rates with a reference treatment. While increased MTLP concentrations in offspring originating from both polluted and unpolluted populations upon exposure indicates a plastic tolerance mechanism, survival and growth rates remain largely unaffected, independent of the population of origin. However, MTLP and Cd concentrations were not significantly correlated. We suggest that MTLP production may be an important mechanism enabling P. saltans populations to persist in ecosystems polluted with heavy metals above a certain level.
... In addition, pollution driven changes in absolute and relative species abundance (e.g., Read et al. 1998; Lock et al. 2003) are expected to result in an overall reduction in suitable prey availability, which furthers constrains the total energy budget. In a study on the wolf spider Pirata piraticus, Hendrickx et al. (2003) showed that populations inhabiting metal polluted sites exhibited life-history characteristics that confirm the reduction in resource acquisition . Key life-history traits such as reproductive output were negatively related with average metal body burden. ...
... Study system and spider maintenance Male and female P. piraticus (Araneae: Lycosidae) were collected in 2 populations in Flanders (Belgium): 1) Damvallei (53°03#N,3°50#E), an unpolluted freshwater marsh henceforth referred to as the reference population (R); 2) Galgenschoor (51°18#N,4°18#E), a tidal marsh located along the river Scheldt, heavily polluted by nearby industrial activities, referred to as the polluted population (P). These populations were selected based on earlier studies where they were shown to be 2 extremes of a lifehistory trait and pollution gradient (Hendrickx et al. 2003). Under natural conditions, adult females produce 1 or 2 egg sacs (May– August) with larger females breeding earlier in the season and showing larger clutch volumes and masses (Hendrickx et al. 2003). ...
... These populations were selected based on earlier studies where they were shown to be 2 extremes of a lifehistory trait and pollution gradient (Hendrickx et al. 2003). Under natural conditions, adult females produce 1 or 2 egg sacs (May– August) with larger females breeding earlier in the season and showing larger clutch volumes and masses (Hendrickx et al. 2003). In an earlier mating experiment, where females were presented with different males on subsequent days and copulation was not prevented, females almost consistently mated only once (in only 6% of 150 mating trials, a female remated after being fertilized) (Eraly D, unpublished data). ...
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When populations face different environmental conditions, both local adaptation and phenotypic plasticity may cause interpopulation divergence of behavioral or phenotypic properties on which mate choice is based. If sustained, this may result in genetic differentiation even in the presence of extant gene flow. Condition dependence of mate choice is one of the main mechanisms explaining these environmental effects. We tested whether experimental food stress affects mate choice in male and female Pirata piraticus spiders from one heavily polluted and one unpolluted reference population. Compared with control females, food-stressed females from the reference population showed a decreased probability of copulation and preferred smaller mates. Females from the polluted population, in contrast, did not show a significant response to food stress and showed size-assortative mating, most strongly under food stress. We explain these results in 2 complementary ways. First, spiders from populations that are not adapted to cope with stress may be less willing to mate when eggs are not fully matured. Second, food-deprived females may show a larger responsiveness toward smaller males because the latter resemble prey more and hungry females tend to attack moving objects more often. Results from this study support the prediction that variation in body condition, driven by local ecological factors, may affect mating behavior and may ultimately lead to population divergence in important life-history traits such as body size. Copyright 2009, Oxford University Press.
... population structure, ecosystem dynamics, and climate change) influence the life cycle of animals (Menzel 2002;Schwartz 2003). For spiders, the term phenology has been employed to describe the life cycle of individuals (Wise 1984;Paquin & Dupérré 2001;Nieto-Castañeda et al. 2012), the age structure of populations over time (Hendrickx & Maelfait 2003;Romero & Vasconcellos-Neto 2003, 2005a, the seasonality of the reproductive period of studied species (Buddle & Draney 2004;Miliczky et al. 2008), and the proportion of males to females within a population (Romero & Vasconcellos-Neto 2005b). ...
... The order Araneae is considered to be mega-diverse, with 46,058 known species (Turnbull 1973;Wise 1993;Adis & Harvey 2000;World Spider Catalog 2016); in spite of that, studies on the population dynamics and phenology of species within this order remain scarce. In addition, most studies focus on species inhabiting temperate regions, where climatic variables seem to determine the life cycle characteristics of spiders (Merrett 1967;Chatzaki et al. 1998) belonging to the families Araneidae (Viera et al. 2003), Lycosidae (Humphreys 1976;Pickavance 2001;Hendrickx & Maelfait 2003), Eresidae (Crouch & Lubin 2000), Linyphiidae (Wise 1984;Buddle & Draney 2004) and Theridiidae (Viera et al. 2007). In the Neotropical region, population dynamics studies have been conducted, for example, on Peucetia viridans (Oxyopidae) (Arango et al. 2000), Misumenops argenteus (Thomisidae) (Romero & Vasconcellos-Neto 2003), Psecas capoda, and P. viridipurpureus (Salticidae) (Rossa-Feres et al. 2000;Romero & Vasconcellos-Neto 2005b), and on some spiders of the family Lycosidae (González et al. 2014). ...
... In most seasonal climates, adult males are present only for two to three months (Hendrickx & Maelfait 2003;Viera et al. 2007), whereas the presence of S. cocheleti males was much longer (half of the year). Probably the prolonged time span of maturation of males is due to the continued presence of adult females. ...
Article
Over a two-year period, we conducted population studies of Selenops cocheleti inhabiting trunks of Plinia cauliflora (Myrtaceae) and Pinus elliottii (Pinaceae) in southeastern Brazil. Adult females were present year-round while adult males were only present during summer, indicating a “stenochronous summer” phenological pattern. The longevity of adult females enables them to continuously generate egg-sacs throughout the year, resulting in the permanent recruitment of individuals. In conclusion, this study provides new insights into the life-history of S. cocheleti and how climatic variables and prey abundance influence the population abundance of the different age classes and adult sexes.
... Although wolf spiders were examined preferentially (e.g. Merret 1968;Costa 1995;Framenau 1998;Marshall et al. 2002;Hendrickx and Maelfait 2003;Cera and Spuņģis 2011;Dolejš et al. 2012), studies on the web-building ones are almost none existent (Sordi 1996). ...
... The most common approach to phenology is the description of periodic life-cycle events for a species or group of species, either in plants (Fenner 1998;Ferreira-Nunes et al. 2012) or animals such as birds (Cotton 2003;Stervander et al. 2005), insects (Wolda 1998;Forkner et al. 2008), scorpions (Araújo et al. 2010) or spiders (Costa 1991;Marshall et al. 2002;Costa et al. 2006). However, the search of variants in phenological patterns among populations of a species is scarce for plants and animals in general (Peterson 1995;Monteiro and Furness 1998;Figuereido-Goulart et al. 2005) and spiders are no exception (Hendrickx and Maelfait 2003;Fernández-Campón 2010). Populations of a species with different phenological patterns can lead to speciation, especially if the temporal location of the sexual periods between them differ, generating reproductive isolation (Monteiro and Furness 1998;Kirkpatrick and Ravigne 2002;Hendrickx and Maelfait 2003;Santos et al. 2007). ...
... However, the search of variants in phenological patterns among populations of a species is scarce for plants and animals in general (Peterson 1995;Monteiro and Furness 1998;Figuereido-Goulart et al. 2005) and spiders are no exception (Hendrickx and Maelfait 2003;Fernández-Campón 2010). Populations of a species with different phenological patterns can lead to speciation, especially if the temporal location of the sexual periods between them differ, generating reproductive isolation (Monteiro and Furness 1998;Kirkpatrick and Ravigne 2002;Hendrickx and Maelfait 2003;Santos et al. 2007). However, this relationship between phenological patterns and speciation does not always occur, depending on other factors such as the magnitude of the temporal isolation between the sexual periods or the existence of intermediate phenological patterns that make gene flow possible, at least indirectly (Peterson 1995). ...
Article
Comparisons of phenological patterns among populations within a species are uncommon in arachnids. Aglaoctenus lagotis is a wolf spider that lives in funnel-webs across South America. The aim of this study was to describe the phenological patterns of two distant populations of A. lagotis (central Argentina, CA, and southern Uruguay, SU). Individuals of each population were sighted along transects, every month for two years. The CA and SU populations differed in their phenological patterns (Wald χ2 = 966.94, df = 66; p <0.001). The CA population showed a spring–summer unified reproductive season and immature individuals overwintered. SU showed the sexual period during autumn, the maternal period during spring–summer and the females, mostly mated, overwintered. These strong differences imply temporal isolation in mating possibilities between both populations. The differences encountered could be due to phenotypic plasticity or have a phylogenetic basis. Interpopulation studies of other features of A. lagotis would show whether they also vary, suggesting speciation.
... We have identified spiders with egg sacs and spiderlings in winter, which is undoubtedly the most convincing proof of the influence of thermal water on the life cycle of spiders. According toHendrickx and Maelfait (2003), adults of Pirata piraticus are present between April and September, reproduction taking place in May–August. We collected a female of Pirata piraticus with an egg sac and another with spiderlings in February (air temperature below 0°C) at Livada de Bihor, where the habitat consists of a channel with flowing warm water originating from a factory. ...
... It is likely that Pirata piraticus inhabits this moist habitat throughout the year, having a continuous growth and development with adult and immature individuals present all the time and having perhaps two or more generations in a year, but additional studies are required to clarify these issues. The high number of juveniles and subadults of Pardosa and Pirata/Piratula collected is due to the fact that the species of these genera generally overwinter in immature stages (e.g.Kiss and Samu 2002;Hendrickx and Maelfait 2003). Some studies on winter-active spiders have reported a high number of Pardosa instars of different stages present on snow especially in mild weather (Huhta and Viramo 1979;Hågvar and Aakra 2006), where they can arrive from the snow-free patches of ground or climbing along the trunks of woody vegetation (Hågvar and Aakra 2006)from the Journal of Natural History 679 overwintering shelters consisting of grass tussocks (Bayram and Luff 1993), leaf litter (Edgar 1971) etc. ...
... The individuals from thermal habitats remaining active during the cold season also have an advantage in development compared with overwintering conspecifics because of a longer growing period (Hågvar and Aakra 2006). Even if they do not attain maturity during winter, they feed and grow further and will be the first that become sexually active in spring and reproduce, the larger individuals reproducing at the beginning of the breeding season (Hendrickx and Maelfait 2003). Taking into account that Pardosa amentata generally overwinters in the subadult stage (Jensen et al. 2011) and the species of this genus seem not to reach adulthood in autumn (Kiss and Samu 2002) it is possible that due to the higher temperatures from thermal habitats some individuals of Pardosa amentata and Pardosa proxima, being active later, moulted and attained sexual maturity at a time when their conspecifics from 'usual' habitats were already/still in dormancy. ...
Article
Shores of channels with thermal water provide an adequate microclimate for maintaining wolf spiders in activity during winter. Of the spiders collected after the winter survey of 22 thermal habitats from western Romania, 93.02% were juveniles and subadults, while the remaining individuals belonged to the following seven species: Arctosa leopardus, Pardosa amentata, Pardosa proxima, Pirata piraticus, Piratula latitans, Trochosa robusta and Trochosa ruricola. The reproductive period of some species is altered under the influence of neighbouring hot waters, as revealed by the capture of females with egg sacs and spiderlings, during winter.
... Reproductive traits can vary between species, between populations of a certain species, and between individuals of a population (e.g., Fox and Czesak, 2000; Fischer et al., 2002; Moya-Laraño, 2002; Høye and Hammel, 2010). Variations in reproductive traits are controlled by a number of factors that include maternal fitness and environmental conditions (Simpson, 1995; Hendrickx and Maelfait, 2003). However, environmental factors such as temperature and food supply can also interact with intrinsic factors like maternal size (Azevedo et al., 1996; Bauerfeind and Fischer, 2008). ...
... Other climatic factors are not considered relevant for unidirectional trends with elevation. Evolutionary theory suggests that harsher environments (e.g., alpine areas) can lead to a trade-off between separate life history traits (Hendrickx et al., 2003; Norry et al., 2006). For several invertebrates, it has been shown that fitness-related traits, including characteristics of life cycle and reproduction, can vary along latitudinal and along elevation climatic gradients (David and Bocquet, 1975; Berven and Gill, 1983; Dingle et al., 1990; Ayres and Scriber, 1994; Tatar et al., 1997; Telfer and Hassall , 1999; Lencioni, 2004; Hodkinson, 2005; Samietz et al., 2005). ...
... For several invertebrates, it has been shown that fitness-related traits, including characteristics of life cycle and reproduction, can vary along latitudinal and along elevation climatic gradients (David and Bocquet, 1975; Berven and Gill, 1983; Dingle et al., 1990; Ayres and Scriber, 1994; Tatar et al., 1997; Telfer and Hassall , 1999; Lencioni, 2004; Hodkinson, 2005; Samietz et al., 2005). Lycosid spiders (i.e., wolf spiders) are well-suited model organisms for various aspects of (spider) ecology, including the influence of environmental conditions on spiders (see, e.g., Hendrickx and Maelfait, 2003; Löffler and Finch, 2005; Høye et al., 2009; Høye and Hammel, 2010), because they colonize a huge variety of terrestrial habitats from sea level to high alpine areas. Thus, wolf spiders have become the most intensively studied spider family to date (Wise, 1993, 2006). ...
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Differentiations in reproductive traits along climatic gradients can be substantial for a species to spread along a wide spatial range. We compared the reproductive effort allocated to first egg sacs of five species of the genus Pardosa: P. palustris (Linnaeus 1758), P. amentata (Clerck 1757), P. lugubris (Walckenaer 1802), P. hyperborea (Thorell 1872), and P. riparia (C. L. Koch 1833) along three elevation transects in central Norway. We tested whether population differences are consistent among the three transects, respectively along the elevational gradient. We assumed that the harsh environments of alpine areas would lead to adaptations in reproductive traits resulting in larger eggs but smaller clutches at higher elevations. The results show that female size and egg number were positively correlated among all species. However, no clear elevation-related trend was found. Other traits did not change consistently between species and along the elevational gradient. We assume that local microclimatic impacts on spider fitness are a crucial but poorly understood factor. Without further knowledge about adaptation and phenotypic plasticity in ectotherms, modeling of possible future reproduction biology might remain flawed.
... Specifically, we wanted to determine in ovo development of three tundra-dwelling sympatric wolf spiders, whether body size or condition better explained variation in fecundity and relative reproductive effort (RRE), a ratio of female body mass to clutch mass, and to test if a trade-off exists between investment in offspring size and number. We predicted that female body size would be the best predictor of fecundity (Simpson 1993; Buddle 2000; Hendrickx and Maelfait 2003; Reed and Nicholas 2008), and that female body condition would best predict the relative reproductive effort (Blueweiss et al. 1978; Brown et al. 2003) of each female because condition is likely a better indicator of available resources that females can allocate to individual eggs. By condition, we mean body mass independent of size (i.e., the residual index; Jakob et al. 1996). ...
... This is a commonly used measure of individual offspring size (e.g., Simpson 1993, Brown et al. 2003); in addition, Hendrickx and Maelfait (2003) determined that the mass of the silk cocoon itself contributed negligibly to the total egg-sac mass. We tested whether there were significant egg size and number trade-offs within species within each site using linear models of the residuals of fecundity and the residuals of mean individual egg mass (Simpson 1995; Hendrickx and Maelfait 2003). Densities of the three focal species were estimated using a ring of hard plastic measuring 1.13 m in diameter (1 m × 1 m area) and about 12 cm high. ...
Article
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We studied populations of three tundra-dwelling wolf spider (Lycosidae) species to determine reproductive trait relationships and developmental timing in the Arctic. We collected 451 Pardosa lapponica (Thorell, 1872), 176 Pardosa sodalis Holm, 1970, and 117 Pardosa moesta Banks, 1892 during summer 2008. We used log-likelihood ratio tests and multiple linear regressions to determine the best predictors of fecundity and relative reproductive effort. Female body size best explained the variation in fecundity and body condition was the best predictor for relative reproductive effort. We tested for a trade-off between the allocation of resources to individual eggs and the number of eggs produced (fecundity) within each species using linear regression. There was variation in detectable egg size and number trade-offs among sites and these may be related to local variation in resource allocation linked to density-related biotic or abiotic factors. These findings contribute to knowledge about the fitness of arctic wolf spiders in the region of study and are particularly relevant in light of the effects that climate changes are predicted to have on the arctic fauna.
... Beside the preference for beneficial structural and microclimatic conditions, there is evidence that microhabitat selection is af-fected by the size or diversity of a community (Marshall and Rypstra 1999) as well as by food availability Wise 1997, Toft and. In addition, there is often a shift of habitat utilization caused by changing requirements of the species due to seasonality, reproduction, or life cycles (Hendrickx andMaelfait 2003, Berg andBengtsson 2007). Hence, microhabitat heterogeneity and its spatial and temporal dynamic play an important role in determining the local spider distribution pattern, as well as the closely related population and ecosystem processes Kareiva 1997, Leibold et al. 2004). ...
Article
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Spiders contribute essentially to the arthropod community of forests and are known to be distributed in non-random pattern according to environmental, structural, competitive, and predacious conditions. The aim of the study was to investigate the effects of the distance to trees on the distribution pattern of soil-dwelling spiders. We verified the hypothesis that stem-close and stem-distant microhabitats differ with respect to taxonomical and ecological characteristics of spider assemblages, hence, functional significance on a small spatial scale. Ground-dwelling spiders were collected with pitfall traps in positions close (20-30 cm) and distant (2 m) to the stem bases in mature forests of different stand types (spruce, Douglas fir, beech-spruce, oak-beech). To identify significant drivers of spider assemblage composition, environmental parameters were assessed in relation with the arrangement of pitfall traps. The study documented significant variability in the composition of spider assemblages of stem-close and stem-distant pitfall traps within each of the study sites. The position of traps strongly affected species richness, species composition, activity density, and dominance structure. Thus, sampling at both positions revealed that the species richness of spiders is spatially restricted. Moreover, spider assemblage structure differed in the classification of species to size and ecological preference. Those results implicate potential consequences for their functional role in forests in relation to the distance to the trees.
... Eggs were larger, presumably reflecting a higher content in lipids (Anderson 1990; Moya-Laraño et al. 2008) but in lower numbers to increase offspring fitness in unfavorable habitats, whereas in favorable habitats, eggs were smaller but more numerous to increase female fecundity. Some studies already showed a trade-off between number and size of eggs (for spiders, see Spence et al. 1996; Brown et al. 2003; Hendrickx and Maelfait 2003), but this trade-off can be hard to detect due to its interference with differences in resource acquisition among populations or individuals (van Noordwijk and de Jong 1986; Walker et al. 2003). A reduced reproductive output can be compensated by increasing offspring size, this strategy being predicted to maximize parental fitness (Hendrickx et al. 2003b). ...
Article
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Current models in evolutionary ecology predict life history alterations in response to habitat suitability to optimize fitness. Only few empirical studies have demonstrated how life history traits that are expected to trade off against each other differ among environments. In Europe, many salt marshes have been recently invaded by the grass Elymus athericus. Previous studies however showed higher densities of the endangered spider Arctosa fulvolineata (Araneae: Lycosidae) in invaded salt marshes compared to natural habitats, which suggests a lower habitat suitability in the latter. The aim of this study was to determine if this emerging habitat (1) affects the amount of resource acquisition and (2) alters the balance between life history traits that are expected to trade off against each other in this stenotopic salt marsh species. As suggested by theoretical studies, an optimization of fitness by increasing egg size at the cost of decreasing fecundity in unsuitable (i.e., natural) habitats was expected. Females presenting cocoon were then collected in close invaded and natural salt marsh areas within the Mont Saint-Michel Bay (France). By considering female mass as covariate, cocoon mass, number of eggs, and egg volume were compared between both habitats. Clutch mass was strongly determined by female mass in both habitats. Clutch mass was however significantly smaller in the natural habitat compared to the invaded habitat, indicating a higher resource acquisition in the latter. When correcting for female size, fecundity was additionally increased in the invaded habitat through a significant decrease in egg size. This phenotypic response can be explained by differences in habitat structure between invaded and natural habitats: the former offers a more complex litter favoring nocturnal wanderers like A. fulvolineata. The existence of such an adaptive reproduction strategy depending on habitat suitability constitutes an original case of an invasion that favors an endangered species.
... body mass relative to body size) is considered a sensitive individual-based measure of stress effects (Danielson-Francois et al., 2002;Aisenberg, 2009). While body size is fixed after maturation (Hagstrum, 1971;Hendrickx and Maelfait, 2003), body mass varies with nutritional status and energetic balance and is often positively correlated with fecundity (Jones and Hopkin, 1998;Danielson-Francois et al., 2002). When energetically stressed, females can be expected to invest in less but larger offspring relative to their own size since the latter generally mature earlier, develop faster and survive better (Van Noordwijk and Dejong, 1986;Stearns, 1992;Fox and Czesak, 2000;Tamate and Maekawa, 2000;Hendrickx et al., 2003b). ...
... The number of eggs in each cocoon was counted and the length and width of ten eggs per cocoon were mea-sured to the nearest 0.01 mm. Egg volume was calculated according to the formula: egg volume = π/6 * (egg length) * (egg width) 2 (Hendrickx and Maelfait, 2003). ...
Article
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Salt-marsh invasions by the grass Elymus athericus (Poaceae) recently transformed usual areas dominated by Atriplex portulacoides (Chenopodiaceae) into homogeneous meadows. Two wolf spider species, Pardosa purbeckensis and A rctosa fulvolineata, show contrasting densities and habitat preferences in salt marshes (respectively dominant and co-dominant ground-living spiders) and oppositely respond to the grass invasion. This allowed us to test whether invasive species that alter habitat structure affect reproduction in addition to previously recorded changes in density. Reproductive traits (female mass, cocoon mass, number and volume of eggs, hatched cocoon as a proxy of reproduction date) were studied in both invaded and natural salt marshes during 2007 and 2008 in the Mont St-Michel Bay (France). In both species, reproductive outputs (cocoon mass) were higher in optimal habitats and volume of eggs was found to be independent from female mass, whereas the latter significantly influenced the number of eggs. In A. fulvolineata, lower reproductive outputs due to less numerous although larger eggs were found in suboptimal habitats whereas the opposite pattern was found in optimal habitats, showing the existence of plastic phenotypic trade-offs in habitats of different qualities. In P. purbeckensis, despite differences in population size among habitats, no reproductive trade-off was found. This study thus shows that two sympatric species belonging to the same family can differ in reproductive strategies and phenotypic plasticity under changes in habitat suitability. (C) Koninklijke Brill NV, Leiden, 2011.
... Therefore, wolf spiders, such as Pardosa species, offer the possibility of studying co-variations between such traits, and sometimes even of investigating potential trade-offs in maternal investment (e.g. Hendrickx and Maelfait 2003;Ameline et al. 2017). ...
Article
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The Arctic tundra is characterised by harsh conditions and environmental gradients are especially pronounced. Variation in functional traits along such gradients provide insights into the drivers of species abundance and distribution and are particularly valuable in this region currently experiencing strong climate warming. Over three consecutive years, we analysed the interacting effect of two environmental factors, habitat and elevation, on the abundance, body size, and clutch size in two common Low-Arctic invertebrate predators (Lycosidae, Araneae), Pardosa furcifera (Thorell 1875) and Pardosa hyperbo-rea (Thorell 1872). Using generalised linear models, we firstly showed a habitat partitioning between P. furcifera, which dominated wet habitats, like fens, and P. hyperborea, which was more associated with drier habitats, like shrubs. Secondly, we found smaller body sizes at high elevation in P. hyperborea, a species that has a southern distribution in Greenland, and we identified season length as a major driver of the development in this species. In P. furcifera, a species likely more cold adapted, we found no body size difference between elevations, suggesting that local conditions (e.g. prey availability or snowmelt timing) are more important in explaining body size variations. Finally, body size and clutch size were strongly correlated in both species, but clutch size was not affected by habitat or elevation. We argue that fecundity is likely influenced by trade-offs and that considering additional complementary trait measurements would allow for a better understanding of the mechanisms underlying patterns in species life-history traits along environmental gradients.
... We were unable to relate clutch size to female body size in our study because nearly all egg sacs became detached in the pitfall traps. We would expect female body size to impact clutch size because body size is typically associated with number of offspring produced (Honěk 1993;Brown et al. 2003;Hendrickx and Maelfait 2003;Hein et al. 2015Hein et al. , 2018, including in P. glacialis in Greenland (Ameline et al. 2018;Høye et al. 2020). In addition, there could be hidden effects on clutch size if female size impacts the probability of producing an egg sac. ...
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Aquatic insects are often consumed by terrestrial predators in Arctic tundra. However, this aquatic-terrestrial linkage may be disrupted by rapid warming that is causing a decrease in freshwater habitats across large areas of the Arctic. In this study, we investigated emerging mosquitoes (Diptera: Culicidae) as a resource subsidy for wolf spiders (Araneae: Lycosidae) in western Greenland, an area where significant pond drying has occurred in recent decades. We used pitfall trapping to compare the abundance, size, and fecundity of wolf spiders collected near (< 1 m) versus far (75–100 m) from the margins of three tundra ponds before, during, and after mosquito emergence. Nearly 90% of the wolf spiders collected in our study were Pardosa glacialis, the species that subsequently became the focus of our analyses. P. glacialis abundances, sizes, and the proportion of females with an egg sac were similar throughout the season both near and far from ponds. However, females near ponds produced about 20% more eggs per egg sac. Stable isotope analyses and a laboratory experiment confirmed mosquito consumption by P. glacialis and demonstrated that individuals collected near tundra ponds were significantly depleted in 13C relative to those in upland habitats, indicating differences in food resources among habitats. Our evidence indicates that mosquitoes do indeed serve as a subsidy to wolf spiders in western Greenland, but the demographic effects on spiders appear to be modest. Thus, P. glacialis abundance in the landscape may be relatively robust to pond drying and associated biotic and abiotic changes. Further studies will be needed to assess the broader effects for tundra ecosystems of disruptions to this and other aquatic-terrestrial linkages via the drying of ponds.
... Regularly, males and females engaged in a face-to-face "jousting" interaction with their front legs and pedipalps during courtship, before copulation. Previous work on P. piraticus does not mention this "jousting" behavior (Felton 1969;Hendrickx & Maelfait 2003;Eraly et al. 2009). In addition, it is interesting to note that all previous data collected on P. piraticus has been from populations in Europe and Asia. ...
Poster
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Wolf spider species (Lycosidae) have been well studied in North America due to their abundance and exciting copulatory behavior. At times aggressive, this behavior can range from chasing and biting, to cannibalism in some species such as Schizocosa ocreata (Persons & Uetz 2005). While collecting fishing spiders (Pisauridae) with Dr. Steven K. Schwartz (Gonzaga University) during summer 2016, I collected Pirata piraticus (Clerck 1758), initially thinking they were juvenile Dolomedes triton (Walckenaer 1837). However, this initial observation was quickly challenged when we found a female individual carrying an egg sac. Upon closer inspection of additional “juvenile” spiders we found that most were actually adult P. piraticus females. This led me to conduct mating trials with P. piraticus. During their courtship, an interesting behavior was observed for all P. piraticus pairs. Regularly, males and females engaged in a face-to-face “jousting” interaction with their front legs and pedipalps during courtship, before copulation. Previous work on P. piraticus does not mention this “jousting” behavior (Felton 1969; Hendrickx & Maelfait 2003; Eraly et al. 2009). In addition, it is interesting to note that all previous data collected on P. piraticus has been from populations in Europe and Asia. There are no studies, to our knowledge, that have been conducted using North American P. piraticus populations.
... Our results provide the first evidence of an Arctic spider species being able to produce two clutches. This is demonstrated by a striking bimodal frequency distribution of clutch sizes in the wolf spider P. glacialis, which is indicative of second clutches in temperate regions [32,45]. Moreover, clutches with fewer eggs (47 eggs or less) were produced significantly later in the season than larger clutches. ...
Preprint
Spiders at southern latitudes commonly produce multiple clutches, but this has not been observed at high latitudes where activity seasons are much shorter. Yet the timing of snowmelt is advancing in the Arctic, and may allow some species to produce an additional clutch. To determine if this is already happening, we used specimens of the wolf spider Pardosa glacialis caught by pitfall traps from the long-term (1996-2014) monitoring program at Zackenberg, Northeast Greenland. We dissected individual egg sacs and counted the number of eggs and partially developed juveniles, and measured carapace width of the mothers. Upon discovery of a bimodal frequency distribution of clutch sizes, as is typical for wolf spiders at lower latitudes producing a second clutch, we assigned egg sacs to being a first or second clutch depending on clutch size. We tested whether the median capture date differed among first and second clutches, whether clutch size was correlated to female size, and whether the proportion of second clutches produced within a season was related to climate. We found that assigned second clutches appeared significantly later in the season than first clutches. In years with earlier snowmelt, first clutches occurred earlier and the proportion of second clutches produced was larger. This result, likely a result of female spiders producing first clutches earlier in those years, which allowed time for another clutch. Clutch size for first clutches was correlated to female size, while this was not the case for second clutches. Our results provide the first evidence for Arctic invertebrates producing additional clutches in response to warming. This could be a common but overlooked phenomenon due to the challenges associated with long-term collection of life history data in the Arctic. Moreover, given that wolf spiders are a widely distributed, important tundra predator, we may expect to see population and food web consequences of their increased reproductive rates.
... Our results provide the first evidence of an Arctic spider species being able to produce two clutches. This is demonstrated by a striking bimodal frequency distribution of clutch sizes in the wolf spider P. glacialis, which is indicative of second clutches in temperate regions [32,45]. Moreover, clutches with fewer eggs (47 eggs or less) were produced significantly later in the season than larger clutches. ...
Article
Spiders at southern latitudes commonly produce multiple clutches, but this has not been observed at high latitudes where activity seasons are much shorter. Yet the timing of snowmelt is advancing in the Arctic, which may allow some species to produce an additional clutch. To determine if this is already happening, we used specimens of the wolf spider Pardosa glacialis caught by pitfall traps from the long-term (1996-2014) monitoring programme at Zackenberg, NE Greenland. We dissected individual egg sacs and counted the number of eggs and partially developed juveniles, and measured carapace width of the mothers. Upon the discovery of a bimodal frequency distribution of clutch sizes, as is typical for wolf spiders at lower latitudes producing a second clutch, we assigned egg sacs to being a first or second clutch depending on clutch size. We tested whether the median capture date differed among first and second clutches, whether clutch size was correlated to female size, and whether the proportion of second clutches produced within a season was related to climate. We found that assigned second clutches appeared significantly later in the season than first clutches. In years with earlier snowmelt, first clutches occurred earlier and the proportion of second clutches produced was larger. Likely, females produce their first clutch earlier in those years which allow them time to produce another clutch. Clutch size for first clutches was correlated to female size, while this was not the case for second clutches. Our results provide the first evidence for Arctic invertebrates producing additional clutches in response to warming. This could be a common but overlooked phenomenon due to the challenges associated with long-term collection of life-history data in the Arctic. Moreover, given that wolf spiders are a widely distributed, important tundra predator, we may expect to see population and food web consequences of their increased reproductive rates.
... In contrast to Pardosa, Pirata was more frequently captured in riparian habitats than in agricultural fields during the seasonal activity study. This is consistent with previously observed preferences of Pirata for moist habitats (Graham et al. 2003, Hendrickx and Maelfait 2003, DeVito et al. 2004). Activity-abundance data from the directional movement study suggest that Pirata is most abundant in the interior riparian buffer throughout the summer. ...
Chapter
Compared to insects, relatively few arachnids have adapted to life in fresh water. The majority of these are mites (Acari), but a few species of spiders (Araneae) use the surface film as a hunting area, with even fewer venturing under water. Members of dozens of families of mites live on and below the water's surface in lentic and lotic habitats of all varieties, including phytotelms, hot springs, rushing rivers and deep lakes. Although invasion of fresh water has occurred dozens of times in the Acari, and include predatory, herbivorous and detritivorous species, the majority of these mites belong to the Hydrachnidiae, the 'true' water mites. Most water mites have a complex life cycle involving a larval stage parasitic on insects, and predatory nymphal and adult stages. Although there is good evidence that parasitism and predation by water mites can influence population dynamics of hosts and prey, and that they are diverse and ecologically sensitive members of freshwater communities, water mites (and other freshwater mites) are often excluded from surveys of freshwater invertebrates. In addition to providing an overview of the diversity and ecology of freshwater mites, this chapter includes methods for collection, rearing and observation that should help with future studies of the biology of these interesting and still mysterious animals.
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Life history trade-offs are a key notion in evolutionary biology, notably for understanding how selection shapes the diversity of traits among species. Despite the frequent study of such trade-offs, few studies synchronously investigate the effects of multiple factors, such as niche specialization and adaptation to harsh environments. We compared reproduction (fecundity and egg quality) in two sympatric couples (one habitat generalist and one specialist) of con-generic wolf spider species, in both Arctic and temperate habitats. We found that specialist species at both latitudes invested more in clutch size than did generalist species. We interpret this result as an optimization of clutch production. In the Arctic, the specialist was able to invest in fecundity with increasing body size at a much higher rate than the generalist species. In the temperate habitat, both species showed similar strategies: they increased quantity and quality of offspring relative to body size at the same rate. These results are consistent with the hypothesis that Arctic species must develop distinct strategies in order not to overlap each other's ecological niches as a consequence of limited food resources or niche space. We emphasize the need to test the role of plasticity and environmentally mediated effects of competition on arthropod fitness.
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The present study describes the life history of Aglaoctenus lagotis Holmberg, 1876 from oviposition to adulthood, analyzing the number of eggs in each egg sac, birth rate, number of instars, sex ratio, cephalothorax size of all instars, and developmental time in laboratory. The results indicate that the studied species can produce two egg sacs during the reproductive period, and that the post-embryonic phase includes 12 nymphal instars. A higher mortality rate was observed during the first three instars, featuring a Type III survival curve. The sex ratio was geared towards the female in the adults and no significant difference was observed in the length of the cephalothorax between male and female. This species can therefore be considered monomorphic. Sexual dimorphism was observed in the cuticle color, with males being light brown whereas females are dark brown.
Article
Abstract 1. Life-history traits and density were assayed in seven populations of two sympatric species of wolf spider for three consecutive years. The goal of the study was to quantify population dynamics and its relation to spatial and temporal life-history variation. 2. Adult female body size and fecundity varied significantly, among field sites and among years, in both species. Female spiders of both species differed in mean relative reproductive effort among sites, but not among years. The size of offspring was invariable, with no significant differences due to site or year. 3. All populations of both species tended to either decrease or increase in density during a given year and this was tightly correlated with changes in prey consumption rates. 4. Since life-history patterns are determined primarily by selection, it is concluded that size at sexual maturity for females is phenotypically plastic and responds to changes in prey availability. Offspring size however is not plastic and it is likely that other selection forces have determined offspring size. Temporal fluctuations in population size are correlated over a large area relative to dispersal capabilities for these species and conservation efforts for invertebrates must take this into consideration.
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Environmental gradients can help us comprehend the range of adaptations or plasticity that a given species can exhibit in response to climatic change. In this study, we assessed the response in female body size, clutch size and egg volume to elevational gradients in closely related wolf spiders. We measured these traits in Pardosa glacialis, P. hyperborea, P. furcifera and P. palustris, collected along elevational gradients across six sites in Arctic and sub-Arctic regions (four sites in Greenland, one in Iceland and one in the Faroe Islands), although not all species were found at all sites. Body size and reproductive traits did not vary with elevation in a consistent manner among species although smaller species were more sensitive to the gradients. The positive relationship between body size and clutch size was most pronounced in the larger species, indicating that larger species are better able to translate favourable environmental conditions into a larger reproductive output. Our study illustrates that elevational gradients may not fully capture spatial variation in environmental conditions experienced by high-latitude wolf spider species.
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Body size is one of the most important individual traits, determining various other life-history traits, including fitness. Both evolutionary and ecological factors shape the body size in arthropods, but the relative contribution of abiotic drivers acting at different spatial scales has been little investigated. We aimed to identify the importance of two broad-scale variables (study region and elevation) in shaping body size of the free-running and locally abundant wolf spider Pardosa palustris (Linnaeus 1758), in contrast to the fine-scaled variable topographic position. Therefore, we set up transects along environmental gradients in the arctic-alpine ecosystems of Norway, which we analyzed using a random forest approach to identify the relative importance of topographic position, elevation, and study region on body size of P. palustris. Our approach revealed that research region was the best explanatory variable, followed by elevation and topographic position. Differences in body size were most likely a consequence of the pronounced differences in season length and the ability of P. palustris to avoid local unfavorable environmental conditions due to its high mobility.
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The habitat and distribution of some closely related species of the P. lugubris s.l. group in Belgium are described to contribute to our understanding of the coexistence and speciation of these 'cryptic' species. With a few exceptions, P. lugubris has its main distribution in the lower part of Belgium where it occurs on sandy, nutrient poor soils. P. saltans occurs widely in Belgium except for in the Campine region where the species is totally absent. P. alacris was only found at three localities where limestone outcrops are present. The habitat of P. lugubris is pine and birch forests while in Fagus woodlands, only P. saltans was found. In Quercus forests, both species were found, often in mixed populations. A combination of micro- and macroclimatological features and habitat characteristics cause the differences in distribution of these species.
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Univariate computation of residuals or allometric variates should be used to estimate the shape of body parts of ectothermic vertebrates. For studies involving more than one group, three types of relationships may be used to calculate the slopes or allometric coefficients necessary for computing the shape variate: pooled group, common-within groups, and individual-within groups. For both residuals and allometric variates, the pooled and common-within groups coefficients resulted in similar estimates of shape when there was no between-group heterogeneity in relationships. Within-group coefficients resulted in quite different estimates of shape. Heterogeneity of slopes or allometric coefficients resulted in different estimates of shape for the same individual for pooled common-within and within-groups data. Such differences in the shape variates were cumulative in subsequent analyses such that considerably different biological interpretations of group interrelationships resulted. Thus, if any between-group heterogeneity exists in regression or allometric relationships, it is imperative that shape be estimated from the common-within groups relationship.
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Summary Spiders have been extensively used as ecological indicators in nature conservation and management in Flanders (Belgium). Recently, research projects have been set up to assess the effects of heavy metal pollution and habitat fragmentation on spider populations. From the first results of these studies, it seems that spiders could be good bio-indicators for evaluating the impact of these anthropogenic disturbance factors on natural ecosystems.
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We conducted a food supplementation field experiment to test two hypotheses: (1) fecundity of the fishing spider Dolomedes triton is limited by a shortage of prey, and (2) the increased movement of adult female D. triton exhibited upon maturation is a foraging adaptation to lessen the impact of food limitation on egg production. Free ranging, uniquely marked adult female fishing spiders were assigned either to a food-supplemented group that received crickets in addition to their natural diet, or to a control group. Juvenile female spiders were also marked and their movement patterns were recorded, but juveniles were not offered supplemental food. Food-supplemented adult females gained weight at a faster rate and hatched more than twice as many offspring as control females. Adult females in the control group moved greater distances per day than did juvenile females. Supplemented adult females moved shorter distances per day than control females, and the movement pattern of fed adults did not differ from that of juveniles. These results support the hypotheses that adult female D. triton are food limited, and that the increased movement of adult females is a switch in foraging behavior that occurs during the reproductive period. Our finding that natural prey shortages limit egg production contrasts with laboratory-based studies of food limitation in the genus Dolomedes, and contradicts a basic assumption of a recent hypothesis that sexual cannibalism in Dolomedes is non-adaptive. These discrepancies highlight the importance of insights gained from field experiments with natural populations.
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Cannibalistic tendencies are well known in spiders and may be a significant factor influencing population size. The wolf spider, Pardosa agrestis, is the dominant non-web-building spider in a wide range of central European agricultural habitats. Preliminary field observations indicated an extended reproductive period, which results in a very wide size distribution of juvenile instars. We hypothesised that if cannibalism is enhanced by differences in size, especially during periods when prey is scarce, these populations might be susceptible to cannibalism in an ecologically significant way. Laboratory studies were conducted on juvenile P. agrestis in arenas. We analysed the following specific aspects of cannibalism: (1) the effect of the weight ratio between the opponents; (2) the effect of weight per se, and (3) the role of hunger level in determining cannibalistic tendencies of spiders. The role of weight and hunger were analysed in separate experiments, in both cases by controlling for the other variable. The results showed that cannibalism was strongly positively correlated with both weight ratio and hunger, but absolute size/age of an individual could not predict the occurrence of a cannibalistic event. These experiments generated the plausible hypothesis that cannibalism might be an important phenomenon in the regulation of real populations, which should be tested specifically in future field experiments.
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Most models of optimal progeny size assume that there is a trade-off between progeny size and number, and that progeny fitness increases with increasing investment per young. We find that both assumptions are supported by empirical studies but that the trade-off is less apparent when organisms are iteroparous, use adult-acquired resources for reproduction, or provide parental care. We then review patterns of variation in progeny size among species, among populations within species, among individuals within populations, and among progeny produced by a single female. We argue that much of the variation in progeny size among species, and among populations within species, is likely due to variation in natural selection. However, few studies have manipulated progeny environments and demonstrated that the relationship between progeny size and fitness actually differs among environments, and fewer still have demonstrated why selection favors different sized progeny in different environments. We argue that much of the variation in progeny size among females within populations, and among progeny produced by a single female, is probably nonadaptive. However, some species of arthropods exhibit plasticity in progeny size in response to several environmental factors, and much of this plasticity is likely adaptive. We conclude that advances in theory have substantially outpaced empirical data. We hope that this review will stimulate researchers to examine the specific factors that result in variation in selection on progeny size within and among populations, and how this variation in selection influences the evolution of the patterns we observe.
Chapter
The fitness of organisms is the primary focus of evolutionary biology. Since the fittest are those which provide more descendants to future generations than their competitors, and fitness is largely determined by the age-dependent schedule of behavior, birth, death, and development rates, life histories are adaptations of unique importance to the analysis of Darwinian evolution (Stearns 1976; Bell 1980). Life history characters covary and function together, and so constitute complex adaptations because they are interdependent (Frazetta 1975). Such sets of covarying traits are often referred to as “strategies” or “tactics” in the literature of ecology and evolution, meaning that they are “coadapted traits designed, by natural selection, to solve particular ecological problems” (Stearns 1976). Because of their relation to fitness, a great deal of theory, experiment, and field study has been directed at determining which associations of life history traits will evolve under particular ecological conditions.
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The density, fecundity, and life-cycle of Pardosa moesta Banks 1892 and Pardosa mackenziana (Keyserling 1877) were studied in a deciduous forest in central Alberta, Canada. Density estimates were lower than reported for other Pardosa species; they ranged from 0.46 per m2 for male P. mackenziana to 2.99 per m2 for immature P. mackenziana. Adult female densities were below 1 per m2 for both species. Clutch sizes were highly variable and averaged (± SE) 33.06 ± 1.29 for P. moesta and 48.37 ± 1.67 for P. mackenziana. Although clutch size was positively related to female size, little of the variation was adequately explained by female size alone. Several lines of evidence suggest that P. moesta and P. mackenziana require two years to mature in central Alberta, with a peak reproductive period in May and June. Females carry egg sacs into the summer months and immature spiders overwinter following the first growing season when they are still less than 5 mg in weight. After a second summer of growth, subadults overwinter and maturation occurs early in the spring.
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(1) The life cycle and population structure of a burrow inhabiting wolf spider, Geolycosa godeffroyi, were examined in the Australian Capital Territory. The phenology of the life cycle was similar to that of the much smaller lycosid, Lycosa (Pardosa) lugubris, in Scotland. The females produced egg sacs in the summer and the young from these egg sacs over-wintered twice before maturity, about fifteen instars later. These females died by the end of the third winter. (2) The burrowing habit of the spiders enabled the field determination of growth rates and of fecundity. The females produced an average of 1f8 cocoons, each containing an average of 338 eggs. About 7.8% of the eggs were estimated to die before the spiderling stage. (3) Two periods of parasite induced mortality occurred, the first in the eggs, caused by scelionid hymenoptera and the second at size classes 11 and 12, caused by acrocerid dipterans. (4) The population was estimated using a combination of quadrat counts and trapping over a period of 599 days. No spiders were removed permanently from the population. The population was divided into fifteen size classes on the basis of the field-determined growth increment through the instars. (5) A stationary age distribution was indicated in the population. (6) The number of spiders passing through each size class was used to estimate the mortality of the spiders. The spiders had a fairly constant size class specific mortality of 3400. The general mortality schedule, although unexpected, was similar to those derived for other spiders and resulted in a Slobodkin Type III survivorship curve.
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The relationship between the energy expended per offspring, fitness of offspring, and parental fitness is presented in a two-dimensional graphical model. The validity of the model in determining an optimal parental strategy is demonstrated analytically. The model applies under various conditions of parental care and sibling care for the offspring but is most useful for species that produce numerous small offspring which are given no parental care.
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A continuous, analytical model of the selection of size-number compromises is presented and applied to the selection of the amount of parental investment in each offspring until its independence. At the evolutionarily stable strategy, the proportional gain in the success of an offspring from an increment in the investment in the offspring equals the proportional loss in offspring numbers. A parallel marginal-value theorem applies to discontinuous variation in the amount of care. When selection acts directly on offspring size rather than on number, the evolutionarily stable level of care depends only on the fitness curve relating the fitness of single offspring to the amount of resources received. General conditions for brood reduction are described. A more-specific rapid-gain version of the continuous model suggests that the amount of parental care is influenced primarily by the level of care at which offspring success increases rapidly. -from Author
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I investigated the relationship between clutch size, female size and mass, and clutch mass in two species of arctic spiders, Alopecosa hirtipes and Pardosa glacialis (Araneae: Lycosidae). Female mass and number of young were significantly correlated with female size in both years of the study. Cocoon mass was significantly correlated with female size in 1991 only. These results are discussed within the context of reproductive trade-offs and models of reproductive effort based on size.
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The mean carapace width (logarithm) shows a linear relationship to stadium for 8 families and 14 species of spiders. Laboratory data from the literature for 4 families and 8 species are plotted to illustrate the point. The rate of increase in mean carapace width shows a linear relationship to sample date for field-collected Tarentula kochi Keyserling, although the slope changes between stadia VI and VII and stadia IX and X (3 regression equations). The carapace width of T. kochi increases 0.15 and 0.32 mm per stadium between stadia I through VI and VII through XII, respectively. The duration of a stadium was calculated by dividing the increase in carapace width between molts by the slope of the regression equation. The calculated duration of stadia I through VI, VII through IX and X through XII was 27.3, 29.6, and 56.1 days per stadium, respectively, for T. kochi in the field. When a 4°C warmer mean microclimate temperature was considered, the duration of stadia I through VI, VII through IX, and X through XII was 29, 35.6, and 55 days per stadium respectively, as predicted from laboratory-rearing data. In addition, regression equations of weight against carapace width for T. kochi and Aptostichus atomarius Simon were similar. The regression equation of weight to carapace width is very useful in relating mean weight of spiders in the field to stadium or size.
Article
The density, fecundity, and life-cycle of Pardosa moesta Banks 1892 and Pardosa mackenziana (Keyserling 1877) were studied in a deciduous forest in central Alberta, Canada. Density estimates were lower than reported for other Pardosa species; they ranged from 0.46 per m2 for male P. mackenziana to 2.99 per m2 for immature P. mackenziana. Adult female densities were below 1 per m2 for both species. Clutch sizes were highly variable and averaged (± SE) 33.06 ± 1.29 for P. moesta and 48.37 ± 1.67 for P. mackenziana. Although clutch size was positively related to female size, little of the variation was adequately explained by female size alone. Several lines of evidence suggest that P. moesta and P. mackenziana require two years to mature in central Alberta, with a peak reproductive period in May and June. Females carry egg sacs into the summer months and immature spiders overwinter following the first growing season when they are still less than 5 mg in weight. After a second summer of growth, sub-adults overwinter and maturation occurs early in the spring.
Article
Pardosa lugubris in Scotland has a 2-year life-cycle. In Holland the situation is less clear-cut: spiderlings emerging from the summer egg sac can reach sexual maturity by the following spring. These spiders, with a 1-year life-cycle, have one instar fewer than the Scottish spiders. The Dutch spiderlings from the autumn egg sac, like the Scottish spiders, have a 2-year life-cycle and have the same number of instars as the Scottish spiders. The shorter life-cycle of some of the Dutch spiders is probably due to the fact that summer temperatures are higher in Holland than in Scotland. It is suggested that the length of the life-cycle may be an important factor in spider distribution and that this may account for the relative scarcity of large spider species in high latitudes.
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The occurrence of different forms of asymmetry complicates the analysis and interpretation of patterns in asymmetry. Furthermore, between-individual heterogeneity in developmental stability (DS) and thus fluctuating asymmetry (FA), is required to find relationships between DS and other factors. Separating directional asymmetry (DA) and antisymmetry (AS) from real FA and understanding between-individual heterogeneity in FA is therefore crucial in the analysis and interpretation of patterns in asymmetry. In this paper we introduce and explore mixture analysis to (i) identify FA, DA and AS from the distribution of the signed asymmetry, and (ii) to model and quantify between-individual heterogeneity in developmental stability and FA. In addition, we expand mixtures to the estimation of the proportion of variation in the unsigned FA that can be attributed to between-individual heterogeneity in the presumed underlying developmental stability (the so-called hypothetical repeatability). Finally, we construct weighted normal probability plots to investigate the assumption of underlying normality of the different components. We specifically show that (i) model selection based on the likelihood ratio test has the potential to yield models that incorporate nearly all heterogeneity in FA; (ii) mixtures appear to be a powerful and sensitive statistical technique to identify the different forms of asymmetry; (iii) restricted measurement accuracy and the occurrence of many zero observations results in an overestimation of the hypothetical repeatability on the basis of the model parameters; and (iv) as judged from the high correlation coefficients of the normal probability plots, the underlying normality assumption appears to hold for the empirical data we analysed. In conclusion, mixtures provide a useful statistical tool to study patterns in asymmetry.
Article
To examine the importance of covariance between stages in traits related to foraging, we quantified the relationships between reproductive success and sizerelated variability in weight gain in juvenile and adult instars of the crab spider Misumenoides formosipes (Araneae: Thomisidae). Prereproductive weight and fecundity are both highly correlated with carapace width, a linear measure of size which does not change within an instar. In field populations, adult females with larger carapaces gain more weight and are more likely to reproduce than females with smaller carapaces. The growth rate of spiders fed ad libitum in the laboratory is unrelated to size, suggesting that size-related differences in the field are due to variation in prey-capture success. Adult females with a carapace width less than 3.4 mm comprised 22% of the population, but were never found to reproduce. Of the individuals that did reproduce, a 17% increase in carapace width resulted in a 100% increase in fecundity. Juvenile stages must be examined to understand adult foraging and reproductive success, because the net weight gained by juvenile instars determines adult size. The final weight gained by spiders in the antepenultimate and penultimate instars explained nearly all the variation in carapace width in the penultimate and adult instars, respectively. We found that constraints on foraging in late juvenile stages are different from the adult stage. Penultimate foraging behavior differs from that of adults, because of constraints on foraging in the period preceding ecdysis. Additionally, in both late juvenile instars, carapace width had little or no effect on the final weight gained within the instar suggesting that factors that affect foraging are different between the juvenile and adult stages. These analyses stress the fact that to fully understand the effects of foraging on reproductive success, we must examine stage-specific constraints throughout an organism's life history.
Article
Adult size and fecundity, total reproductive biomass, egg size, and spiderling size and resistance to desiccation were compared in three populations of the communal orb-weaving spider,Metepeira spinipes, in Mexico. In a desert population and in one from a moist tropical forest adult size, fecundity, and total reproductive biomass were similar, but were markedly smaller than in a climatologically intermediate agricultural habitat. Egg size and protein content were greater in the desert and agricultural habitats than in the moist forest, but spiderling size increased from desert to agricultural to moist forest populations. Desert spiderlings survived significantly longer than moist forest spiderlings at all humidity treatments over a 10% to 100% range. An explanation for these results is proposed based on apparent differences in energy allocation and expenditure which arise from the distinct climate, colony structure, and prey and space availability in the three habitats.
Article
1. The amount of food intake during the egg ripening period and the conversion of this food into eggs (biomass and number of eggs) in four Pardosa species is described. The amount of food taken in is dependent on the size of the spider species. Basically the process of conversion of food into egg-biomass is the same for all four species. Thus the size of the spider species mainly determines the number of eggs in the egg-sac. There are however minor differences in efficiency of the process and in dryweight of the eggs between the species. These differences which are discussed complicated the general process of food conversion into number of eggs. 2. When food shortages are supplied during the egg ripening period two reactions can be observed: a) All species tend to keep the dry weight of the eggs at a constant level. b) Some species produce the same number of eggs under conditions of small food shortages as under conditions of maximum food supply, using reserve material from the body of the female. In this case the female either shows no increase in body weight or a decrease while others immediately adapt the number of eggs to the quantity of food given. Under conditions of strong food shortages, however, both groups of species show the same reaction.
Article
Reproductive success and growth rate data were collected for individually marked crab spiders Misumena vatia (Clerck) in 1980, 1981, and 1982. All measures of reproductive success were found to be quite variable between individuals within years, but did not differ between years. Reproductive effort (mass of clutch/prereproductive mass of female) was the least variable measurement and was not correlated with female weight at reproduction. Clutch weight and number of eggs per clutch were highly correlated with female reproductive weight. Egg weight was not correlated with the number of eggs per clutch. Hatching success did not vary with clutch size and averaged 94.5%. Growth rates of spiders were highly variable, indicating large variation in feeding rate. In 1981 and 1982, approximately 20% of female spiders were unable to capture enough prey to grow and reproduce. Primary prey species differed in weight and in their contribution to spider egg production. Spiders attacked a larger percentage of bumblebees but captured a larger percentage of honeybees. There was no simple relationship between diet choice and reproductive success. Spiders which selected suboptimal umbels to forage on some or all of the time, however, had significantly lower reproductive success than spiders choosing the best umbels.
Article
Eine positive Korrelation zwischen Gre der Mutter und Zahl der Nachkommen wurde in drei Arten der SpinnenfamilieLycosidae gefunden. Da die Gre der Mutter zum Teil erblich bedingt ist, fhrt diese Korrelation automatisch zu einem Selektionsdruck gegen gesteigerte Krpergre. Die Korrelation ist wahrscheinlich bei vielen Tier- und Pflanzengruppen vorhanden und ist einer der bedeutendsten Faktoren, die die Krpergrenzunahme whrend der Evolution bewirkt haben.
Article
Models investigate the interaction between 3 components of fitness: 1) the intrinsic effect of egg size, 2) the density effect, the effect of the density of competing offspring (including competition with sibs and with non-sibs), and 3) the hierarchy effect, the effect of egg size relative to the sizes of competing eggs laid by other females. The environmental effects considered are the intensities of sib and non-sib competition, the number of egg-laying females, and some aspects of seasonal development. The particular aspects of maternal phenotype examined are foraging efficiency and the gametic reserve available at the time of egg laying (broadly equivalent to female size). -from Authors
Life cycle, habitat choice and distribution of Pardosa amentata (Clerck 1757) in Belgium (Araneae, Lycosidae). C.R. Xième Colloque européenne d'Arachnologie, Bulletin de la Societé scientifique de Bretagne I
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Alderweireldt, M. and J-P. Maelfait. 1988. Life cycle, habitat choice and distribution of Pardosa amentata (Clerck 1757) in Belgium (Araneae, Lycosidae). C.R. Xième Colloque européenne d'Arachnologie, Bulletin de la Societé scientifique de Bretagne I. 7-15.
Contribution to the knowlegde of the arachno- and entomofauna of different woodhabitats. Part I. Sampled habitats, theoretical study of the pitfall method, survey of the captured taxa
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Maelfait, J-P. and L. Baert. 1975. Contribution to the knowlegde of the arachno- and entomofauna of different woodhabitats. Part I. Sampled habitats, theoretical study of the pitfall method, survey of the captured taxa. Biologisch Jaarboek Dodoneae 43: 179-196.
Are two cohorts responsible for the bimodal life history pattern in the wolf spider Pardosa agrestis in Hungary?. Pp 215–221
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Samu, F. Németh, J. Toth, F. Szita, E. Kiss, and B& C. Szinetar. 1998. Are two cohorts responsible for the bimodal life history pattern in the wolf spider Pardosa agrestis in Hungary?. Pp 215–221. In Proceedings of the 17<sup>th</sup> European colloquium of Arachnology, P.A. Selden (ed.), Dorset Press, Edinburgh.
Life histories of eight Danish wetland spiders
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Toft, S. 1979. Life histories of eight Danish wetland spiders. Entomologische Meddedelser 47: 22-32.
Life histories of species in the Pardosa pullata group, a study of ten popu-lations in the Netherlands
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Den Hollander, J. 1971. Life histories of species in the Pardosa pullata group, a study of ten popu-lations in the Netherlands (Araneae, Lycosidae).
Spiders as bioindicators
  • J.-P Maelfait
Maelfait, J.-P. 1996. Spiders as bioindicators. Pp.
Factors affecting cannibalism in the wolf spider Pardosa agrestis (Araneae, Lycosidae)
  • F Samu
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  • Kiss
Samu, F., Toft, S. & B. Kiss. 1999. Factors affecting cannibalism in the wolf spider Pardosa agrestis (Araneae, Lycosidae). Behavioural Ecology and Sociobiology 45:349–354.
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Sokal, R.R. & F.J. Rohlf. 1995. Biometry. Freeman & Co, New York.