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Studies on the evolution of brain size variation usually focus on large clades encompassing broad phylogenetic groups. This risks introducing ‘noise’ in the results, often obscuring effects that might be detected in less inclusive clades. Here, we focus on a sample of endocranial volumes (endocasts) of 18 species of rabbits and hares (Lagomorpha: Leporidae), which are a discrete radiation of mammals with a suitably large range of body sizes. Using 60 individuals, we test five popular hypotheses on brain size and olfactory bulb evolution in mammals. We also address the pervasive issue of missing data, using multiple phylogenetic imputations as to conserve the full sample size for all analyses. Our analyses show that home range and burrowing behaviour are the only predictors of leporid brain size variation. Litter size, which is one of the most widely reported constraints on brain size, was unexpectedly not associated with brain size. However, a constraining effect may be masked by a strong association of litter size with temperature seasonality, warranting further study. Lastly, we show that unreasonable estimations of phylogenetic signal (Pagel’s lamba) warrant additional caution when using small sample sizes, such as ours, in comparative studies.

Anthropogenic ozone depletion has led to a 2–5% increase in ultraviolet B radiation (UVBR) levels reaching the earth's surface. Exposure to UVBR causes harmful DNA damage in amphibians, but this is minimized by DNA repair enzymes such as thermally sensitive cyclobutane pyrimidine dimer (CPD)-photolyase, with cool temperatures slowing repair rates. It is unknown whether amphibian species differ in the repair response to a given dose of UVBR across temperatures. We reared larvae of three species ( Limnodynastes peronii , Limnodynastes tasmaniensis and Platyplectrum ornatum ) at 25°C and acutely exposed them to 80 µW cm −2 UVBR for 2 h at either 20°C or 30°C. UVBR-mediated DNA damage was measured as larvae repaired damage in photoreactive light at their exposure temperatures. Cool temperatures increased DNA damage in two species and slowed DNA repair rate in P. ornatum . The magnitude of DNA damage incurred from UVBR was species-specific. Platyplectrum ornatum had the lowest CPDs and DNA repair rates, and the depressive effects of low temperature on photorepair were greater in L. tasmaniensis . Considering the susceptibility of most aquatic organisms to UVBR, this research highlighted a need to consider the complexity of species-specific physiology when forecasting the influence of changing UVBR and temperature in aquatic ecosystems.

Many aquatically respiring animals inhabiting low pH waters can suffer acute inhibition of ion uptake and loss of branchial (gill) epithelial integrity, culminating in a fatal, rapid loss of body Na+. Environmental calcium levels ([Ca2+]e) are pivotal in maintaining branchial junction integrity, with supplemental Ca2+ reversing the negative effects of low pH in some animals. Tolerance of some naturally acidic environments by aquatic animals is further complicated by low [Ca2+]e, yet many of these environments are surprisingly biodiverse. How these animals overcome the combined damaging actions of low pH and low environmental Ca2+ remains unknown. Here, we examined the effects of [Ca2+]e on the response to low pH in larvae of the highly acid tolerant frog Limnodynastes terraereginae. Acute exposure to low pH water in the presence of low [Ca2+]e increased net Na+ efflux. Provision of additional [Ca2+]e reduced net Na+ efflux, but the effect was saturable. Acclimation to both low and high [Ca2+]e improved the resistance of larvae to Na+ efflux at low pH. Inhibition of apical Ca2+ uptake by ruthenium red resulted in an abrupt loss of tolerance to low pH in larvae acclimated to low pH water. Acclimation to acidic water increased branchial gene expression of the intracellular Ca2+ transport protein calbindin, consistent with a role for increased transcellular Ca2+ trafficking in the tolerance of acidic water. This study confirmed the physiological challenge of low [Ca2+]e on branchial integrity in acidic waters and highlighted a potential role for maintenance of transcellular Ca2+ uptake in the acid tolerance of L. terraereginae.Summary statementTolerance of naturally acidic, dilute, and soft waters by larvae of the frog Limnodynastes terraereginae involves adaptations to the branchial calcium transport pathway which protects intercellular junctions against damage.