Conference Paper
Cranial plasticity in lake-dwelling Astyanax morphotypes corresponds to feeding preference
Powers, A.K., Garita-Alvarado, C., Rodiles, R., Berning, D.J., Gross, J.B. and Ornelas-García, C.P.
Record Number:
4297
Year:
2019
Journal:
AIM 2019
Pages:
49
Abstract:
Abstract: Members of the Astyanax genus demonstrate a remarkable lability in morphological
features. For example, surface-dwelling Astyanax mexicanus invaded caves thousands of years
ago, giving rise to blind, depigmented cavefish. Here, we present a study on two closely-related
species: Astyanax aeneus and A. nicaraguensis, distributed across southern Mexico and Central
America, respectively. Both species mainly inhabit river systems, however, in lake-dwelling forms
we observed two highly divergent morphs originally recognized as different genera based, e.g.
Astyanax and Bramocharax. Recent phylogenetic studies from Mexican lakes suggest that these
morphotypes readily hybridize. Despite genetic similarities, Bramocharax morphs exhibit stark
morphological differences in cranial shape and dentition. We investigated the evolution of several
dynamic cranial traits that vary across morphs collected from four lakes in Mexico and Nicaragua
using geometric morphometrics. We found evidence of an ecomorphological cline from the
northern to southern populations. Southern (Nicaraguan) populations of Bramocharax have an
increase in maxillary teeth, have larger unicuspid teeth, an elongated snout and a streamlined
cranium compared to Astyanax morphs. Northern (Mexican) populations, however, converge on
similar cranial shape and tooth morphology between sympatric Bramocharax and Astyanax
morphs. Based on the disparity in trophic related traits, we reasoned that feeding niche
segregation is larger in the southern lake-dwelling populations in comparison with the northern
ones. Using stable isotope analyses on gut contents, we found that northern populations present
a higher trophic niche overlap, mainly with omnivorous feeding modes, while the southern
populations the Bramocharax morph are largely piscivorous, eating other, smaller fish. Taken
together, these results suggest that the southern population of Bramocharax are built for predation
with streamlined “fusiform” bodies and large teeth. This system, like Astyanax mexicanus, is ideal
for examining phenotypic plasticity in response to environmental pressures. Future genetic
association studies will address the genetic basis underlying predator (unicuspid) versus
omnivore (multicuspid) tooth patterning.
Times Cited:
1
Conference Name:
Astyanax Interrnational Meeting
Relevent Species: