Extreme intra-clutch egg size dimorphism is not coupled with corresponding differences in antioxidant capacity and stable isotopes between eggs

Abstract Sexual size dimorphism (SSD) has long attracted the attention of biologists, and life-history variation is thought to play an important role in the evolution of SSD. Here we quantified SSD and female reproductive traits to identify potential associations between SSD and female reproduction in the white-striped grass lizard Takydromus wolteri. In a population from Chuzhou, China, the largest male and female were 53.0 mm and 57.5 mm in snout-vent length (SVL), respectively. Females were larger in SVL and abdomen length, whereas males were larger in head size and tail length. Females produced up to five clutches of eggs during the breeding season, with large females producing more clutches and more eggs per clutch than small ones. As a result, large females had a higher annual fecundity and reproductive output. Egg size was positively correlated with maternal SVL in the first clutch, but not in subsequent clutches. These results suggest that T. wolteri is a species with female-biased SSD, and that fecundity selection, in which large females have higher fecundity due to their higher capacity for laying eggs, is likely correlated with the evolution of SSD in this species [Current Zoology 58 (2): 236–243, 2012].

Download Full-text

Migratory constraints on yolk precursors limit yolk androgen deposition and underlie a brood reduction strategy in rockhopper penguins

Biology Letters ◽

10.1098/rsbl.2012.0476 ◽

2012 ◽

Vol 8 (6) ◽

pp. 1055-1058 ◽

Cited By ~ 9

Author(s):

Glenn T. Crossin ◽

Maud Poisbleau ◽

Laurent Demongin ◽

Olivier Chastel ◽

Tony D. Williams ◽

...

Keyword(s):

Steroid Hormones ◽

Maternal Effects ◽

Egg Size ◽

Hatching Asynchrony ◽

Brood Reduction ◽

Size Dimorphism ◽

Reduction Strategy ◽

Yolk Androgens ◽

Linear Relationships ◽

Androgen Levels

Hormonally mediated maternal effects link maternal phenotype and environmental conditions to offspring phenotype. The production of lipid-rich maternal yolk precursors may provide a mechanism by which lipophilic steroid hormones can be transported to developing yolks, thus predicting a positive correlation between yolk precursors in mothers and androgen levels in eggs. Using rockhopper penguins ( Eudyptes chrysocome ), which produce a two-egg clutch characterized by extreme egg-size dimorphism, reversed hatching asynchrony and brood-reduction, we examined correlations between circulating concentrations of the primary yolk-precursor vitellogenin (VTG) and levels of yolk androgens. Previous work in Eudyptes penguins has shown that egg-size dimorphism is the product of migratory constraints on yolk precursor production. We predicted that if yolk precursors are constrained, androgen transport to developing yolks would be similarly constrained. We reveal positive linear relationships between maternal VTG and androgens in small A-eggs but not larger B-eggs, which is consistent with a migratory constraint operating on the A-egg. Results suggest that intra-clutch variation in total yolk androgen levels depends on the production and uptake of yolk precursors. The brood reduction strategy common to Eudyptes might thus be best described as the result of a migratory constraint.

Download Full-text