Vrtilek, M. | Search bioRxiv

bioRxiv2020

Egg size does not universally predict embryonic resources and hatchling size across annual killifish species

Egg size has a crucial impact on the reproductive success of a mother and the performance of her offspring. It is therefore reasonable to employ egg size as a proxy for egg content when studying variation in offspring performance. Here, we tested species differences in allometries of several egg content parameters with egg area. We measured individual eggs in five species of annual killifish (Cyprinodontiformes), a group of fish where egg banks permit population survival over dry season. Apart from comparing allometric scaling exponents, amounts and compositions of egg components across the different species, we assessed the explanatory power of egg area for egg wet and dry weight and for hatchling size. We found notable species-specific allometries between egg area and the other egg parameters (egg dry weight and water content, elemental composition and triglyceride content). Across species, egg area predicted egg wet weight with highest power. Within species, coefficients of determination were largest in Austrolebias elongatus, a large piscivorous species with large eggs. Our study shows that systematically using egg area as a proxy of egg content between different species can ignore relevant species-specific differences and mask within-species variability in egg content.

zoology↗

bioRxiv2020

The role of maternal effects on offspring performance in familiar and novel environments

Maternal effects are an important evolutionary force that may either facilitate adaptation to a new environment or buffer against unfavourable conditions. The degree of variation in traits expressed by siblings from different mothers is frequently sensitive to environmental conditions. This could generate a Maternal-by-Environment interaction (MxE) that could inflate estimates of Genotype-by-Environment effects (GxE). We aimed to test for environment-specific maternal effects (MxE) using a paternal full-sib/half-sib breeding design in the seed beetle Callosobruchus maculatus, where we split and reared offspring from the same mother on two different bean host types - original and novel. Our quantitative genetic analysis indicated that maternal effects were very small on both host types for all the measured life-history traits. There was also little evidence that maternal oviposition preference for a particular host type predicted her offsprings performance on that host. Further, additive genetic variance for most traits was relatively high on both hosts. While there was higher heritability for offspring reared in the novel host, there was no evidence for GxEs, and most cross-host genetic correlations were positive. This suggests that offspring from the same family ranked similarly for performance on both host types. Our results point to a genetic basis of host adaptation in the seed beetle, rather than maternal effects. Even so, we encourage researchers to test for potential MxEs because, due to a lack of testing, it remains unclear how often they arise.

evolutionary biology↗