Resumen:
Although different mechanisms exist to explain the presence of polymorphism in
lizards, one model suggests that multiple morphotypes display the same level of fitness.
Three male morphs (grey, yellow and orange) coexist in Sceloporus aeneus, a
Mexican endemic oviparous lizard. Using a histological perspective, we test the hypothesis
that spermatogenic output does not vary across morphotypes of S. aeneus
during its maximum testicular activity. Males of S. aeneus (five grey, five yellow and
five orange) were collected in Calimaya, Estado de México, Mexico. Snout-vent
length (SVL), testis mass, diameter and epithelial heights for the seminiferous tubules
and epididymis, and the number of layers of germ cells did not vary among
morphs; moreover, according to principal component analysis, a high overlap among
lateral colour morphs exists. Our results suggest strongly that the lateral colour
morphs in S. aeneus have the same spermatogenic output, and natural selection may
be a stronger driving force than sexual selection within this species. Further studies
into other lizard species with multiple morphotypes are required to determine whether
the lack of variation in spermatogenic output observed in this endemic lizard is consistent
across polymorphic species which will provide a greater understanding of the
selective mechanisms acting on an individual’s fitness.