Effects of experimentally elevated in ovo testosterone exposure on early chick growth and cell mediated immunity in the Japanese quail Coturnix japonica

Maternal effects may have profound influences on offspring phenotype.  One such effect, the transfer of maternal androgens to eggs, may be an adaptive way for females to enhance offspring growth rates.  Early exposure to androgens, however, may also suppress immunity.  In this study, we experimentally elevated yolk levels of testosterone in the eggs of Japanese quail (Coturnix japonica) via microinjection prior to incubation.  Subsequently we assessed growth and cell mediated immune function in developing chicks.  We predicted that chicks exposed to experimentally elevated testosterone levels would have 1) enhanced post-hatching growth rates relative to controls and 2) suppressed cell-mediated immunity relative to controls.  Contrary to our predictions, there was no influence of testosterone treatment on chick growth or cell-mediated immunity.  The potential implications of these results are discussed within the context of previous studies on the transfer of maternal androgens to eggs.

Heidinger, B. J. and Grindstaff J.L. 2002.  Integrative and Comparative Biology.  42 (6): 1242-1243

Parental care and clutch sizes in North and South American birds

The evolutionary causes of small clutch sizes in tropical and Southern Hemisphere regions are poorly understood. Alexander Skutch proposed 50 years ago that higher nest predation in the south constrains the rate at which parent birds can deliver food to young and thereby constrains clutch size by limiting the number of young that parents can feed. This hypothesis for explaining differences in clutch size and parental behaviors between latitudes has remained untested. Here, a detailed study of bird species in Arizona and Argentina shows that Skutch's hypothesis explains clutch size variation within North and South America. However, neither Skutch's hypothesis nor two major alternatives explain differences between latitudes.

Martin TE, Martin PR, Olson CR, Heidinger BJ, Fontaine JJ. 2000.  Science.  287 (5457): 1482-1485.