Every gain comes with loss: Ecological and physiological shifts associated with polyploidization in a pygmy frog.

Abstract

Polyploidization plays a pivotal role in vertebrate evolution and diversification. However, the effects of polyploidization on animals across various biological levels, and how these differences drive ecological shifts, remain unclear. Through karyotype analysis and whole-genome sequencing, we identified an autotetraploid Microhyla fissipes from Hainan Island, which shows reproductive isolation and geographic differentiation from its diploid counterpart. Tetraploids exhibited larger cell size, improved tadpole growth rates, and greater whole-body size, along with reduced cell cycle activity. Rather than being simple scaled-up diploids, tetraploids showed shifts in physiological performance, organ allometry, gene expression profiles, and metabolic patterns. Tetraploid adults demonstrated superior jumping ability and increased reproductive investment (e.g., larger gonads and steeper slopes in the relationship between gonadal weight and body weight), suggesting a potential competitive advantage over diploids. However, tetraploids exhibited higher energy expenditure at elevated temperatures, reduced hepatic energy storage, and altered pulmonary regulatory metabolites at 25 oC. Males had smaller relative heart sizes, and females showed flatter slopes in the relationship between heart and lung weight and body weight, indicating reduced investment in cardiopulmonary system. These variations suggest an increased risk of metabolic constraints under heat stress, putting tetraploids at a disadvantage in warmer regions. Importantly, the physiological trade-offs associated with polyploidization help explain the geographical differentiation between diploids and tetraploids, which reflects a climatic boundary, with tetraploids occupying cooler northeastern areas. Our findings identify an autotetraploid frog, report the first autotetraploid genome in amphibians, and demonstrate how vertebrate polyploids physiologically and ecologically diverge from their diploid counterparts.