Intraspecific developmental variation in the life cycle of the Andean Treefrog (Boana riojana): A temporal analysis

Intraspecific variation during the anuran larval period has been analyzed mainly in relation to the timing of metamorphosis and body size at metamorphosis. However, other traits may vary as well. We examined two developmental series of Boana riojana from the same population in two consecutive years and describe intraspecific variation in larvae of this species. We discuss how variation, if present, may influence its life cycle. We found that both larval series differed in the larval period length, one twice as long as the other. This variation primarily depended on when breeding occurred, metamorphosis was achieved during late spring in both generations and at similar sizes, and only the rate of larval development during premetamorphosis varied extensively between years. This is consistent with thyroid gland activity because when it became active the developmental trajectory became more canalized. No variation of staging sequence occurred in relation to the different durations of the larval period. However, in the long-lasting series we found two different morphs. Also, integument, thyroid gland, skeleton, and testis differentiation events occurred at the same developing stages. In contrast, ovarian differentiation proceeded at the same absolute age in both series. Sexual dimorphism becomes evident within the year after metamorphosis. The intraspecific heterochrony that we describe for the larval development of B. riojana does not lead to phenotypic variation at the end of metamorphosis. We discuss the importance of analyzing growth and development independently. Each proceeds differently in time, but with an interdependence at some point, because size and shape do not vary at the end of metamorphosis.