Why do cold animals make bigger babies?

Reproduction involves a critical decision: Should an organism invest energy in a few large offspring or many small ones? In a new study from The American Naturalist, Michael Angilletta (Indiana State University), Chris Oufiero (University of California, Riverside), and Adam Leaché (University of California, Berkeley) used a new statistical approach that can test multiple theories at the same time, an approach they hope will shed light on many evolutionary problems. They used data from many populations of Eastern Fence Lizards (Sceloporus undulatus), which revealed that the lizards in colder environments produce larger offspring than lizards in warmer environments.

So why do animals in colder climates produce larger offspring? One theory suggests the larger size of offspring counteracts their slow growth in the cold. Yet another theory suggests large offspring are not directly linked to temperature at all. Instead, large offspring just happen to be produced by large mothers, who grow large because they require more energy to reproduce in the cold.

When they tested the theories simultaneously with their new approach, the team concluded that temperature's effect on reproduction is a byproduct of its effect on adult size. "This result could have widespread significance," says Angilletta. "Temperature determines the adult size of virtually all organisms. For many of these organisms, we expect temperature to also leave an imprint on reproduction." Source : University of Chicago Press Journals