Genetic Basis of Differential Heat Resistance between Two Species of Congeneric Freshwater Snails: Insights from Quantitative Proteomics and Base Substitution Rate Analysis

We compared the heat tolerance, proteomic
responses to heat stress,
and adaptive sequence divergence in the invasive snail Pomacea
canaliculata and its noninvasive congener Pomacea
diffusa. The LT50 of P. canaliculata was significantly higher than that of P. diffusa. More than 3350 proteins were identified from
the hepatopancreas of the snails exposed to acute and chronic thermal
stress using iTRAQ-coupled mass spectrometry. Acute exposure (3 h
exposure at 37 °C with 25 °C as control) resulted in similar
numbers (27 in P. canaliculata and 23 in P. diffusa) of differentially expressed proteins in the
two species. Chronic exposure (3 weeks of exposure at 35 °C with
25 °C as control) caused differential expression of more proteins
(58 in P. canaliculata and 118 in P. diffusa), with many of them related to restoration of damaged molecules,
ubiquitinating dysfunctional molecules, and utilization of energy
reserves in both species; but only in P. diffusa was
there a shift from carbohydrate to lipid catabolism. Analysis of orthologous
genes encoding the differentially expressed proteins revealed two
genes having clear evidence of positive selection (Ka/Ks > 1) and
seven candidates for more detailed analysis of positive selection
(Ka/Ks between 0.5 and 1). These nine genes are related to energy
metabolism, cellular oxidative homeostasis, signaling, and binding
processes. Overall, the proteomic and base substitution rate analyses
indicate genetic basis of differential resistance to heat stress between
the two species, and such differences could affect their further range
expansion in a warming climate.