Life-history correlates of the evolution of live bearing in fishes

Abstract

Selection for live bearing is thought to occur when the benefits of increasing offspring survival exceed the costs of reduced fecundity, mobility and the increased metabolic demands of carrying offspring throughout development. We present evidence that live bearing has evolved from egg laying 12 times in teleost (bony) fishes, bringing the total number of transitions to 21 to 22 times in all fishes, including elasmobranchs (sharks and rays). Live bearers produce larger offspring than egg layers in all of 13 independent comparisons for which data were available. However, contrary to our expectation there has not been a consistent reduction in fecundity; live bearers have fewer offspring in seven out of the 11 available comparisons. It was predicted that live bearers would have a larger body size, as this facilitates accommodation of developing offspring. This prediction was upheld in 14 out of 20 comparisons. However, this trend was driven by elasmobranchs, with large live bearers in seven out of eight comparisons. Thus, while the evolution of live bearing in elasmobranchs is correlated with predicted increases in offspring size and adult size, teleost live bearers do not have such a consistent suite of life-history correlates. This suggests that constraints or selection pressures on associated life histories may differ in live-bearing elasmobranchs and teleost fishes.

Reproduction of the Blacktip Shark in the Gulf of Mexico

“…While the relationships were not strong, they provide more evidence that elasmobranchs become more fit reproductively as they grow and age (Baremore and Hale 2012), assuming that senescence is not a factor. The prevailing theory of elasmobranch reproductive biology is that the increase in body size allows for an increase in fecundity Musick 2001, 2012;Goodwin et al 2002). However, it stands to reason that, like teleost fishes, older elasmobranchs may be able to devote more energy to reproduction and therefore produce more fit offspring.…”

Global-scale predictions of community and ecosystem properties from simple ecological theory

“…For elasmobranchs, we assessed biomass and production for coastal and oceanic species, where coastal species were defined as those inhabiting depths less than or equal to 200 m. This distinction was based on differences in the life history and distribution of these groups. Oceanic epipelagic species living away from shelf areas but typically at depths less than 200 m (Compagno in press) were assumed to be present in all body mass classes greater than or equal to 10 3.55 (consistent with a mean size at birthZ3258 gG2.6 g 95% CI, nZ15, data from Goodwin et al 2002). It was assumed that oceanic epipelagic elasmobranchs accounted for 20% of numbers in body mass class 10 4.05 (midpointZ11 220 g) and that all species would be present in this class.…”

“…The value of a was set as 5.75 and b as 0.2. Coastal elasmobranchs that live on shelves to 200 m depth are smaller at birth (meanZ221 gG1.3 g 95% CI nZ167, data from Goodwin et al 2002) and were allocated to all classes greater than 10 2.35 . They were assumed to account for 10% of numbers in class 10 2.95 .…”

Does more maternal investment mean a larger brain? Evolutionary relationships between reproductive mode and brain size in chondrichthyans

“…The greatest number of gains and losses of maternal investment (matrotrophy) in vertebrates has occurred in the chondrichthyans, where matrotrophy has evolved four or five times and has potentially been lost 7-9 times (Dulvy and Reynolds 1997). In contrast, matrotrophy has evolved only four times in teleosts and appears never to have been lost (Wourms 1994;Goodwin et al 2002). In fishes, including chondrichthyans, there appear to be few ecological correlates with reproductive mode; for example, there are no differences in the biogeographic distributions of live-bearers and egg-layers that cannot be explained by the differences in body size (Goodwin et al 2005).…”