Data from: Oxygen limitation at the larval stage and the evolution of maternal investment per offspring in aquatic environments
Rollinson, Njal; Rowe, Locke (2017), Data from: Oxygen limitation at the larval stage and the evolution of maternal investment per offspring in aquatic environments, Dryad, Dataset, https://doi.org/10.5061/dryad.h6qp4
Many selective agents have been implicated in the evolution of maternal investment per offspring. Although oxygen limitation and surface-area-to-volume relationships were historically thought to constrain investment in individual eggs in aquatic environments, a weight of evidence now indicates that egg size per se does not influence oxygen availability to embryos. Yet, larval size is related to egg size, and hence investment per offspring, thus the scaling of oxygen assimilation efficiency with larval size may still constrain investment per offspring in aquatic environments. We employ comparative methods in the Amphibia to investigate this problem. We demonstrate that the slope of species-mean egg diameter over habitat temperature is negative for species with aquatic larvae, and the decline in egg size is similar whether eggs are laid terrestrially or aquatically. Further, the slope of egg diameter over temperature is more negative for species with aquatic larvae compared to species that feature terrestrial eggs and no larvae. Finally, we show that egg size declines with temperature more strongly for species whose larvae cannot breathe aerially prior to metamorphosis, compared to those that can. Our results suggest that oxygen transport in larvae, not eggs, constrains investment per offspring in aquatic systems. This study also helps reconcile conflicting reports that undermined the generality of temperature-dependent oxygen limitation as a mechanism driving the temperature-size rule in aquatic systems.