Resurrecting the differential mortality model of sexual size dimorphism

Mas, Eva De; Ribera, Carles; Moya-Laraño, Jordi

doi:10.1111/j.1420-9101.2009.01786.x

Cited by 24 publications

(9 citation statements)

References 78 publications

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“…For example, the Differential Mortality Model predicts that smaller males are favored because the high predation risk that males suffer during mate searching relaxes male-male contest competition for females, and ultimately selection favoring large males. This in turn favors early maturation because it improves male viability and his chances to reproduce [15,58]. Certainly, direct selection favoring smaller bridging males and indirect viability selection also favoring smaller males can work synergistically.…”

Section: Discussionmentioning

confidence: 99%

“…Thus, when the SDIcw and SDImass are large and positive (large females), the SDIbp is predicted to be large and negative (males bridge more than females). In the second approach we followed the method used by De Mas et al [58], which is an adaptation of Smith's suggestion for analyzing SSD through multiple regression using log-transformed variables and introducing statistical control [73]. As we did in the previous analysis, we introduced the average for each sex and species in the multiple regression model.…”

Section: Methodsmentioning

confidence: 99%

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Introducing the refined gravity hypothesis of extreme sexual size dimorphism

et al. 2010

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BackgroundExplanations for the evolution of female-biased, extreme Sexual Size Dimorphism (SSD), which has puzzled researchers since Darwin, are still controversial. Here we propose an extension of the Gravity Hypothesis (i.e., the GH, which postulates a climbing advantage for small males) that in conjunction with the fecundity hypothesis appears to have the most general power to explain the evolution of SSD in spiders so far. In this "Bridging GH" we propose that bridging locomotion (i.e., walking upside-down under own-made silk bridges) may be behind the evolution of extreme SSD. A biomechanical model shows that there is a physical constraint for large spiders to bridge. This should lead to a trade-off between other traits and dispersal in which bridging would favor smaller sizes and other selective forces (e.g. fecundity selection in females) would favor larger sizes. If bridging allows faster dispersal, small males would have a selective advantage by enjoying more mating opportunities. We predicted that both large males and females would show a lower propensity to bridge, and that SSD would be negatively correlated with sexual dimorphism in bridging propensity. To test these hypotheses we experimentally induced bridging in males and females of 13 species of spiders belonging to the two clades in which bridging locomotion has evolved independently and in which most of the cases of extreme SSD in spiders are found.ResultsWe found that 1) as the degree of SSD increased and females became larger, females tended to bridge less relative to males, and that 2) smaller males and females show a higher propensity to bridge.ConclusionsPhysical constraints make bridging inefficient for large spiders. Thus, in species where bridging is a very common mode of locomotion, small males, by being more efficient at bridging, will be competitively superior and enjoy more mating opportunities. This "Bridging GH" helps to solve the controversial question of what keeps males small and also contributes to explain the wide range of SSD in spiders, as those spider species in which extreme SSD has not evolved but still live in tall vegetation, do not use bridging locomotion to disperse.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Introducing the refined gravity hypothesis of extreme sexual size dimorphism

et al. 2010

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“…The foraging -mortality trade-off is predicted because females probably expose themselves to predators or potentially dangerous prey to a greater extent than males (Mikolajewski et al 2005, Verdolin 2006). Males on the other hand probably suffer from a high mortality as adults during mate search (Andrade 2003, De Mas et al 2009, Kasumovic et al 2007, but see Fromhage et al 2007), and hence are expected to be under strong viability selection to survive to adulthood (Vollrath and Parker 1992). Indeed, the operational and effective sex ratios are male-biased in A. aurantia (Foellmer 2008), and may be so in other similar systems as well (Fromhage et al 2007, Miller 2007.…”

Section: Discussionmentioning

confidence: 99%

Sex-Specific Foraging Behaviours and Growth Rates in Juveniles Contribute to the Development of Extreme Sexual Size Dimorphism in a Spider~!2010-03-14~!2010-05-31~!2010-08-13~!

Inkpen¹,

Foellmer²

2010

TOECOLJ

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Extreme sexual size dimorphism (SSD) in temperate species is expected to be proximally caused, at least partially, by sex-specific growth rates due to the limited time available for growth and reproduction. Hence sex-specific foraging strategies are predicted to mediate differential growth rates. However, little is known about how sex differences in foraging behaviour and growth trajectories relate to the expression of pronounced SSD. Here we tested for sex-specific foraging strategies and growth rates in juveniles of the highly size dimorphic orb-web spider Argiope aurantia under natural conditions. In a number of web sites, we estimated web height, web size (size of the prey capture area), mesh size, stabilimentum (web decoration) size and length, vegetation density and prey availability. Over four days in the field we also measured spider growth and web site tenacity. Independently of body size, females exhibited faster growth rate than males. When body size and condition were controlled for, we found that females built larger webs, and at sites with greater prey availability compared to males. Males built webs with significantly larger and longer stabilimenta independent of web size. These results indicate that extreme female-biased SSD in A. aurantia is at least partially the result of sex-specific growth rates already in early juvenile stages mediated by sex-specific web design and placement to allow for greater foraging success of females compared to males. We discuss these findings in the context of SSD evolution, and consider whether the sex-specific behaviours detected are more likely consequences or causes of the evolution of extreme SSD.

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“…On the other hand, male and female spiders in many families often differ significantly in their ecology, with females constructing webs and having a sedentary lifestyle while males may move considerable distances in search of mates [ 89 , 90 , 91 ]. The risk of mortality from visually foraging predators is presumably higher in wandering males than in sedentary females sitting effectively motionless in their webs; hence, selection favors males attaining precocious sexual maturity at an earlier (and smaller) stage in their development than females, which may benefit from larger size by achieving higher fecundity [ 74 , 92 , 93 ]. On the other hand, when competition amongst males for access to mates is high, and/or when both sexes are under similar risks to survival such as predation, then selection may favor an increase in male size and thus reduced SSD [ 92 ].…”

Section: Spiders and Climate Changementioning

confidence: 99%

Climate Change, Extreme Temperatures and Sex-Related Responses in Spiders

Harvey

Dong

2023

Biology

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Climatic extremes, such as heat waves, are increasing in frequency, intensity and duration under anthropogenic climate change. These extreme events pose a great threat to many organisms, and especially ectotherms, which are susceptible to high temperatures. In nature, many ectotherms, such as insects, may seek cooler microclimates and ’ride out´ extreme temperatures, especially when these are transient and unpredictable. However, some ectotherms, such as web-building spiders, may be more prone to heat-related mortality than more motile organisms. Adult females in many spider families are sedentary and build webs in micro-habitats where they spend their entire lives. Under extreme heat, they may be limited in their ability to move vertically or horizontally to find cooler microhabitats. Males, on the other hand, are often nomadic, have broader spatial distributions, and thus might be better able to escape exposure to heat. However, life-history traits in spiders such as the relative body size of males and females and spatial ecology also vary across different taxonomic groups based on their phylogeny. This may make different species or families more or less susceptible to heat waves and exposure to very high temperatures. Selection to extreme temperatures may drive adaptive responses in female physiology, morphology or web site selection in species that build small or exposed webs. Male spiders may be better able to avoid heat-related stress than females by seeking refuge under objects such as bark or rocks with cooler microclimates. Here, we discuss these aspects in detail and propose research focusing on male and female spider behavior and reproduction across different taxa exposed to temperature extremes.

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Resurrecting the differential mortality model of sexual size dimorphism

Cited by 24 publications

References 78 publications

Introducing the refined gravity hypothesis of extreme sexual size dimorphism

Introducing the refined gravity hypothesis of extreme sexual size dimorphism

Sex-Specific Foraging Behaviours and Growth Rates in Juveniles Contribute to the Development of Extreme Sexual Size Dimorphism in a Spider~!2010-03-14~!2010-05-31~!2010-08-13~!

Climate Change, Extreme Temperatures and Sex-Related Responses in Spiders

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