The effect of genetics, diet, and social environment on adult male size in a sexually dimorphic spider

The role of developmental plasticity in the evolution and maintenance of sexual size dimorphism (SSD) has recently received more attention. We experimentally investigated the effects of genetics (pedigree), social cues, and food availability on developmental time and adult male size in Nephilingis cruentata, an extremely female-biased sexually size dimorphic spider with notable male size variation. In a split-brood design, we exposed spiderlings of known pedigrees to either a high or low feeding regime. We tested the males' ability to match the sub-adult growth and time of maturation to the perceived female availability and male competition by exposing them to silk cues of either males or females during the subadult stage. We recorded male size at maturation and total developmental time, the duration of the sub-adult stage, and the growth during the sub-adult stage. Poorly fed males had a longer development and matured at extremely small sizes compared to well-fed males. The social cues did not influence the duration of the sub-adult stage nor the male size at maturation. However, males exposed to male cues grew more and were heavier at reaching maturity than those exposed to female cues, which implies that sub-adult males respond to perceived male-male competition by investing more in growth. Furthermore, variation in male size has been explained by low additive genetic variability but high maternal effects. Our results highlight the role of maternal effects and/or common environment in shaping male body size. Future studies with a scope for maternal effects on SSD are warranted.

Automated summary

This study experimentally investigated the effects of genetics, social cues, and food availability on developmental time and sexual size dimorphism in spiders. The results showed that poorly fed males had longer developmental time and matured at smaller sizes, while social cues did not affect developmental time or mature size. Males exposed to male cues grew more and were heavier, suggesting a response to perceived male-male competition.