Clutch frequency affects the offspring size-number trade-off in lizards

Abstract

Background: Studies of lizards have shown that offspring size cannot be altered by manipulating clutch size in species with a high clutch frequency. This raises a question of whether clutch frequency has a key role in influencing the offspring size-number trade-off in lizards.

Methodology/principal findings: To test the hypothesis that females reproducing more frequently are less likely to tradeoff offspring size against offspring number, we applied the follicle ablation technique to female Eremias argus (Lacertidae) from Handan (HD) and Gonghe (GH), the two populations that differ in clutch frequency. Follicle ablation resulted in enlargement of egg size in GH females, but not in HD females. GH females switched from producing a larger number of smaller eggs in the first clutch to a smaller number of larger eggs in the second clutch; HD females showed a similar pattern of seasonal shifts in egg size, but kept clutch size constant between the first two clutches. Thus, the egg size-number trade-off was evident in GH females, but not in HD females.

Conclusions/significance: As HD females (mean = 3.1 clutches per year) reproduce more frequently than do GH females (mean = 1.6 clutches per year), our data therefore validate the hypothesis tested. Our data also provide an inference that maximization of maternal fitness could be achieved in females by diverting a large enough, rather than a higher-than-usual, fraction of the available energy to individual offspring in a given reproductive episode.

Figure 1. Mean values (+SE) for post-oviposition body mass, clutch size and egg mass of the females involved.

Clutch size for the follicle-ablated females was calculated as the sum of yolking follicles removed and eggs produced. Black, diagonal and open bars represent follicle-ablated, sham-ablated and control females, respectively. White horizontal and vertical lines represent mean and ±SE for the actual number of eggs laid by follicle-ablated HD and GH females, respectively.