Publication Abstract

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

N. B. Goodwin, N. K. Dulvy and J. D. Reynolds

Aim:

To test whether fishes with contrasting reproductive modes (egg-laying versus live-bearing) have different geographic ranges. Live-bearing females can control levels of energetic investment and the rate of development and provide a ‘safe harbour’ at a vulnerable period in the life cycle. Consequently live-born off spring tend to be born large and independent and can be transported across environmental barriers by their parents. Therefore we test the hypothesis that live-bearing offers greater opportunities for species to exploit a wider range of habitats and environments than egg-laying.

Location:

Global, marine and freshwater, teleost and elasmobranch fishes.

Method:

Cross-species comparisons of five different measures of geographic range: list the measures. A phylogenetic comparative approach based on paired comparisons of egg-layers and their closest live-bearing relatives, and a phylogenetic regression between body size and measures of geographic range.

Results:

Cross-species tests show that teleost egg-layers live across a wider range of latitudes than live-bearers but at lower latitudes, across a narrower depth range and at shallow depth. Elasmobranchs show the opposite pattern. Phylogenetic paired comparisons of sister egg-laying and live-bearing taxa also suggest that teleost egg-layers and elasmobranch live-bearers have a larger latitudinal range size; but other measures of geographic range do not differ with reproductive mode. Body size is also correlated with latitudinal range size in all fishes?

Conclusions:

Cross-species comparisons generally support the hypothesis that live-bearing elasmobranchs have a wider geographic range, but not among teleosts. However, species rich groups bias cross-species analyses by inflating sample sizes, and tests do not consider the effects of evolutionary history. The comparative approach provides weak evidence to support the prediction that live-bearers are more widely distributed than egg-layers, but only in elasmobranchs. The taxonomic differences in whether egg-layers or live-bearers have a wider latitudinal range are explained by the positive association between body size and latitudinal range size rather than reproductive mode per se.

Reference:

N. B. Goodwin, N. K. Dulvy and J. D. Reynolds. 2005. Macroecology of live-bearing in fishes: latitudinal and depth range comparisons with egg-laying fishes. Oikos, 110: 209-218