Resumen:
In this study we examined diet, reproduction, and sexual dimorphism in body size of adult Thamnophis
eques. We measured 307 adult snakes within the hydrologic system of High Lerma. Prey was obtained by forced
regurgitation when snakes were collected, and gravid females were housed in the laboratory until parturition.
Females had a longer snout-vent length and shorter tails than males, but there was no difference in total length
between the two sexes. We found no evidence to support the hypothesis that sexual dimorphism is due to differences
in prey size for this species because the sexes did not differ in the type and mass of prey they consumed; however, the
size of gravid females was positively related to the number, but not size and weight, of their offspring. Our results
suggested that sexual size dimorphism in natural populations of T. eques may be determined by fecundity selection
rather than the ecological factors associated with the spectrum of available prey sizes. We also discuss possible
reasons why the sexes did not differ in total length
Descripción:
Although adult T. eques females had a longer SVL
and HL than males, the sexes did not differ in their
diet, and we found that larger females had more
offspring. These results suggest that sexual size
dimorphism in natural populations of T. eques may be
determined by fecundity selection rather than by the
ecological factors associated with the spectrum of
available prey sizes. The lack of intersexual
differences in the slope of the regression between HL
and SVL, and the upward shift in the intercept of the
regression line for females together with the shift
along the common slope toward larger females (data
for larger females do not overlap with the data for
larger males), showed that the larger heads of the
females are probably an outcome of their larger bodies
(SVL) and not of the allometric relationship between
these traits.
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