The "Challenge Hypothesis": Theoretical Implications for Patterns of Testosterone Secretion, Mating Systems, and Breeding Strategies

TLDR

Temporal patterns of testosterone vary across populations and individuals, and the pattern and amplitude of change are more informative for predicting mating systems than absolute levels. The study proposes a model comparing testosterone amplitude changes with male parental care levels. The model links testosterone amplitude changes to the degree of male parental care. Polygynous males are less responsive to social cues than monogamous males, indicating diverse hormonal responses to interactions and plastic neural mechanisms, and evidence from other vertebrates supports the model’s broader applicability.

Abstract

A combination of field and laboratory investigations has revealed that the temporal patterns of testosterone (T) levels in blood can vary markedly among populations and individuals, and even within individuals from one year to the next. Although T is known to regulate reproductive behavior (both sexual and aggressive) and thus could be expected to correlate with mating systems, it is clear that the absolute levels of T in blood are not always indicative of reproductive state. Rather, the pattern and amplitude of change in T levels are far more useful in making predictions about the hormonal basis of mating systems and breeding strategies. In these contexts we present a model that compares the amplitude of change in T level with the degree of parental care shown by individual males. On the basis of data collected from male birds breeding in natural or captive conditions, polygynous males appear less responsive to social environmental cues than are monogamous males. This model indicates that there may be widely different hormonal responses to male-male and male-female interactions and presumably equally plastic neural mechanisms for the transduction of these signals into endocrine secretions. Furthermore, evidence from other vertebrate taxa suggests strongly that the model is applicable to other classes