Sexual Size Dimorphism: Evolution and Perils of Extreme Phenotypes in Spiders

Kuntner, Matjaž; Coddington, Jonathan A.

doi:10.1146/annurev-ento-011019-025032

Cited by 58 publications

(54 citation statements)

References 145 publications

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“…This agrees with our pattern where spider genera with larger body size tend to be species poor, and have generally narrower geographic distributions. We interpret this recovered pattern to be consistent with the predictions of the hypothesis that extreme phenotypes might decelerate speciation and/or cause extinction [59].…”

Section: Discussionsupporting

confidence: 87%

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Machine learning approaches identify male body size as the most accurate predictor of species richness

Čandek

Kuntner

2020

BMC Biol

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Background: A major challenge in biodiversity science is to understand the factors contributing to the variability of species richness-the number of different species in a community or region-among comparable taxonomic lineages. Multiple biotic and abiotic factors have been hypothesized to have an effect on species richness and have been used as its predictors, but identifying accurate predictors is not straightforward. Spiders are a highly diverse group, with some 48,000 species in 120 families; yet nearly 75% of all species are found within just the ten most speciose families. Here we use a Random Forest machine learning algorithm to test the predictive power of different variables hypothesized to affect species richness of spider genera. Results: We test the predictive power of 22 variables from spiders' morphological, genetic, geographic, ecological and behavioral landscapes on species richness of 45 genera selected to represent the phylogenetic and biological breath of Araneae. Among the variables, Random Forest analyses find body size (specifically, minimum male body size) to best predict species richness. Multiple Correspondence analysis confirms this outcome through a negative relationship between male body size and species richness. Multiple Correspondence analyses furthermore establish that geographic distribution of congeneric species is positively associated with genus diversity, and that genera from phylogenetically older lineages are species poorer. Of the spider-specific traits, neither the presence of ballooning behavior, nor sexual size dimorphism, can predict species richness. Conclusions: We show that machine learning analyses can be used in deciphering the factors associated with diversity patterns. Since no spider-specific biology could predict species richness, but the biologically universal body size did, we believe these conclusions are worthy of broader biological testing. Future work on other groups of organisms will establish whether the detected associations of species richness with small body size and wide geographic ranges hold more broadly.

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Section: Discussionsupporting

confidence: 87%

“…A female-biased SSD is highly pronounced in certain groups of spiders, notably orbweavers [60]. Kuntner and Coddington [59] hypothesize that extreme phenotypes may represent evolutionary dead-ends. Although, as speculated above, size may fit this prediction, it seems that SSD as a derived ratio does not.…”

Section: Discussionmentioning

confidence: 99%

Machine learning approaches identify male body size as the most accurate predictor of species richness

Čandek

Kuntner

2020

BMC Biol

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“…Because eye size is a major factor influencing visual performance (Cronin et al, 2014;Kirschfeld, 1976;Land and Nilsson, 2012), body size increases that lead to eye size increases could be utilized for VA improvements (Corral-López et al, 2017). Based on the prevalence of sexual size dimorphisms throughout many animal groups (Kuntner and Coddington, 2020;Lislevand et al, 2007;Parker, 1992;Teder, 2014), VA differences between the sexes may be an under-documented ---yet not uncommon --phenomenon that warrants further consideration and exploration. and 2) been based on smaller sample sizes.…”

Section: Discussionmentioning

confidence: 99%

A sexual dimorphism in the spatial vision of band-winged grasshoppers

Duncan

Salazar

García

et al. 2020

Preprint

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Visual acuity (VA) --- a measurement of the fineness or coarseness of vision --- correlates with the size of an animal, with larger species often possessing sharper vision. However, it is unknown whether the same relationship between visual acuity and size holds within a species when individuals differ consistently and substantially in size, such as through a sexual size dimorphism. Here we examine the visual acuity of three species of sexually dimorphic band-winged grasshoppers, in which females are the larger sex (Arphia pseudonietana, Dissosteira carolina, and Spharagemon equale; total n = 98). Using a radius of curvature estimation method, we find that females have ∼21% finer vision in the most acute region and axis of the eye than do males. Further explorations of the eyes of the species showing the greatest size dimorphism (D. carolina) suggest that this VA dimorphism is driven by females having larger eyes with more ommatidia. In contrast to many flying insects where males have finer vision to acquire mates, our study is one of the first to demonstrate a female-biased sexual dimorphism in acuity. Given the number of species in which females are larger than males, our results suggest that differences in VA between the sexes may be more common than currently appreciated.

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“…Strong sexual dimorphism in size with large females and small males occurs in many orb web spiders (Foellmer and Moya-Larano 2007;Robinson and Robinson 1973). The most extreme case of reversed sexual size dimorphism among terrestrial animals can be found in the family Nephilidae (Kuntner and Coddington 2020), where tiny males enter the web of a giant female for mating, which then -more often than not -ends with him being a mate and a meal. Spider species with larger males than females are rare (e.g., Lycosidae: Aisenberg et al 2007;Pholcidae: Huber et al 2013;Argyroneta aquatica: Schütz and Taborsky 2003).…”

Section: Morphologymentioning

confidence: 99%

Sex differences in spiders: from phenotype to genomics

et al. 2020

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Sexual reproduction is pervasive in animals and has led to the evolution of sexual dimorphism. In most animals, males and females show marked differences in primary and secondary sexual traits. The formation of sex-specific organs and eventually sex-specific behaviors is defined during the development of an organism. Sex determination processes have been extensively studied in a few well-established model organisms. While some key molecular regulators are conserved across animals, the initiation of sex determination is highly diverse. To reveal the mechanisms underlying the development of sexual dimorphism and to identify the evolutionary forces driving the evolution of different sexes, sex determination mechanisms must thus be studied in detail in many different animal species beyond the typical model systems. In this perspective article, we argue that spiders represent an excellent group of animals in which to study sex determination mechanisms. We show that spiders are sexually dimorphic in various morphological, behavioral, and life history traits. The availability of an increasing number of genomic and transcriptomic resources and functional tools provides a great starting point to scrutinize the extensive sexual dimorphism present in spiders on a mechanistic level. We provide an overview of the current knowledge of sex determination in spiders and propose approaches to reveal the molecular and genetic underpinnings of sexual dimorphism in these exciting animals.

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Sexual Size Dimorphism: Evolution and Perils of Extreme Phenotypes in Spiders

Cited by 58 publications

References 145 publications

Machine learning approaches identify male body size as the most accurate predictor of species richness

Machine learning approaches identify male body size as the most accurate predictor of species richness

A sexual dimorphism in the spatial vision of band-winged grasshoppers

Sex differences in spiders: from phenotype to genomics

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