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Sexual size dimorphism has evolved via sex-specific trait architecture

Sexual size dimorphism (SSD) occurs when individuals of one sex are larger than those of the opposite sex. In the African hermit spider (Nephilingis cruentata), females are about 80 times heavier than males. How can such a large size difference arise, and how would it be possible to remain adaptive towards possibly dynamic sex-specific size optima when both sexes share common genes (a so-called intralocus sexual conflict)?

According to the theory of quantitative genetics, the presence of a sexually dimorphic trait requires at least a partial resolution of the sexual conflict, and this resolution has been suggested to involve, among other things, sex-specific genetic and developmental control, including sex-specific maternal effects. We examined the genetic architecture of body size in Nephilingis cruentata, estimating the sex-specific importance of genetic and maternal effects on size in laboratory-reared individuals across multiple generations. Model estimates indicate that size variation is predominantly determined by additive genetic effects in females but maternal effects in males, with low correlations between sexes for both components. These results suggest a straightforward mechanism to avoid intralocus sexual conflict and allow emergence and maintenance of SSD via sex-specific architecture of body size and thus its sex-independent evolution.

We are currently preparing a manuscript on the results in collaboration with Dr. Paul Debes (debeslab.com/ ) from the Holar University, Iceland and Dr. Matjaž Kuntner (www.ezlab.si/lab-members) from the National Institute of Biology, Ljubljana, Slovenia.​
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Maternal effects buffer anthropogenic effects in an urban spider
Urban environments pose many challenges for animals, two being increased temperature and pollution. Temperature is a critical factor (especially for ectotherms), and heavy metal toxicity has both short and long term negative effects. The direct effects of both are well understood, but studies on transgenerational effects of maternal exposure on offspring phenotypes, are lacking in invertebrates. Spiders make excellent models for studying transgenerational effects, because they are ectotherms, have short generation times and are top invertebrate predators. We propose to determine whether maternal effects can act as a short term buffer against the effects of increased temperature and heavy metal exposure in Larinioides sclopetarius. We will test whether and how maternal exposure to sub-lethal concentrations of a heavy metal affects offspring phenotype and performance, including resistance to starvation, and whether and how maternal exposure to increased temperatures affects offspring life history traits and behaviour, including their resistance to heat waves. (PhD thesis will be carried out by Rok Golobinek)