Effects of Temperature Regime Through Premetamorphic Ontogeny on Shape of the Chondrocranium in the American Toad, Anaxyrus americanus

Abstract

If one considers the substantial amount of information that exists about phenotypic plasticity in amphibians, it is surprising that few studies have examined abiotic factors that influence phenotype through ontogeny. Phenotypic change and stability of morphology are artifacts of organisms that bear significant relevance to evolution within and among taxonomic groups. Here, we examine development as a phenotypically plastic aspect of larval anurans. Fertilized eggs of the American Toad, Anaxyrus (5 Bufo) americanus (Holbrook, 1836), were obtained from two pairs of adults, and larvae were reared in four temperature treatments (constant Mean, constant High, constant Low, and Fluctuating regime [Low night-High day]); developmental series were collected from each treatment, representing larvae of this species from Gosner Stages 28-40. Cleared and stained larvae were analyzed with landmark-based geometric morphometric methods to facilitate examination of differences in overall shape change of the larval chondrocranium through ontogeny, as a result of developmental temperature or temperature regime. Changes in shape of the chondrocranium and in amount and direction of phenotypic change through ontogeny were found in response to temperature treatment and temperature regime. Mean chondrocranial shape of the Fluctuating regime was more similar to the consensus shape of the overall data set than were those of all other treatments. Given that differences in amount and direction of shape change were observed among these treatments and throughout ontogeny, one should consider the affects of abiotic factors (such as temperature) when rearing larval anurans for studies of developmental morphology. Anat Rec,

Incubation temperature affects development order of morphological features and staging criteria in turtle embryos

“…Yntema, ; Mahmoud, Hess & Klicka, ; Crastz, ; Greenbaum, ). Our results mirror those of previous studies of incubation effects on developmental phenology in amphibians (Jorgensen & Sheil, ; Sheil et al ., ). With our data, we can only speculate about the evolutionary causes of this thermally induced developmental plasticity.…”

Deconstructing cartilage shape and size into contributions from embryogenesis, metamorphosis, and tadpole and frog growth

“…Morphometric studies of amphibian cranial variation typically focus on entire skulls or skull regions at pre-or postmetamorphic stages to address phylogenetic, functional or developmental questions (Emerson, 1985;Larson, 2002Larson, , 2004Larson, , 2005Larson, , 2008Jorgensen & Sheil, 2008;Ponssa & Candioti, 2012). This study in contrast focuses on the individual cartilages of a skull region throughout life, and separates their shape trajectories into phases of pre-and post-metamorphic growth and metamorphosis.…”

Variation in timing of ossification affects inferred heterochrony of cranial bones in Lissamphibia

“…Temperature is known to affect timing (Harkey and Semlitsch 1988) and size at metamorphosis (Bizer 1978), but few studies have documented how differences in temperature regimes can affect the sequence of ossification. Jorgensen and Sheil (2008) utilized geometric morphometrics to study shape change induced by different temperature regimes on Anaxyrus (i.e., Bufo) tadpoles and found that mean chondrocranial shape of those specimens raised under a regime of fluctuating daily temperatures most closely approximated the consensus shape of the overall dataset, perhaps suggesting that a fluctuating regime may be preferred for achieving shape changes in the lab that are like those of the wild condition. However, raising animals under constant temperatures may induce patterns of variation that are not representative of the natural condition.…”