Macroecology of live‐bearing in fishes: latitudinal and depth range comparisons with egg‐laying relatives

Abstract

We examine how fishes with contrasting reproductive modes (egg‐laying versus live‐bearing) differ in geographic range size and distribution. One hypothesis based on dispersal suggests that egg‐laying taxa should occupy a wider range of latitudes than live‐bearing, whereas the opposite prediction has been derived from the idea that enhanced maternal input and a ‘safe harbor’ during development will enable live‐bearers to occupy a wider range of latitudes and depths than egg‐layers. Cross‐species analysis supports the first hypothesis for teleosts, with egg‐layers living in a wider range of latitudes than live‐bearers but at lower latitudes, across a narrower depth range and at shallow depth. However, elasmobranchs show the opposite pattern, live‐bearers having wider latitudinal ranges. Phylogenetic paired comparisons of sister egg‐laying and live‐bearing taxa confirm these contrasting patterns between teleosts and elasmobranchs. However, depth range, maximum latitude and depth do not differ with reproductive mode. Latitudinal range size increases with body size among all taxa. However, only teleosts have a positive relationship between body size and maximum latitude, depth and depth range, but this does not differ between reproductive modes. Egg‐laying elasmobranchs have low dispersal, but live‐bearers have not extended their maximum latitude or depth, despite the benefits of sheltered offspring. The differences in range size between egg‐layers and live‐bearers and the distinction between teleosts and elasmobranchs is consequence of contrasting mechanisms of dispersal and benefits of maternally buffered transport of developing offspring.