Horizontal Transposon Transfer and Its Implications for the Ancestral Ecology of Hydrophiine Snakes.

Daniel Enosi Tuipulotu,Kate L Sanders,Nathan Dunstan,Vicki A Thomson,Alastair J Ludington,Timothy G Amos,Alexander Suh,Richard J Edwards,David L Adelson,James D Galbraith

doi:10.3390/genes13020217

Abstract

Transposable elements (TEs), also known as jumping genes, are sequences able to move or copy themselves within a genome. As TEs move throughout genomes they often act as a source of genetic novelty, hence understanding TE evolution within lineages may help in understanding environmental adaptation. Studies into the TE content of lineages of mammals such as bats have uncovered horizontal transposon transfer (HTT) into these lineages, with squamates often also containing the same TEs. Despite the repeated finding of HTT into squamates, little comparative research has examined the evolution of TEs within squamates. Here we examine a diverse family of Australo–Melanesian snakes (Hydrophiinae) to examine if the previously identified, order-wide pattern of variable TE content and activity holds true on a smaller scale. Hydrophiinae diverged from Asian elapids ~30 Mya and have since rapidly diversified into six amphibious, ~60 marine and ~100 terrestrial species that fill a broad range of ecological niches. We find TE diversity and expansion differs between hydrophiines and their Asian relatives and identify multiple HTTs into Hydrophiinae, including three likely transferred into the ancestral hydrophiine from fish. These HTT events provide the first tangible evidence that Hydrophiinae reached Australia from Asia via a marine route.

Highlights

While similar differences in Transposable elements (TEs) expansions between snake lineages have been lineages have been reported by Castoe et al [22], Yin et al [51] and Pasquesi et al [21], the reported by Castoe et al [22], Yin et al [51] and Pasquesi et al [21], the expansions we expansions we describe here are over much shorter time periods
In our survey of elapid genomes, we have found that TE diversity and their level of expansion varies significantly within a single family of squamates, similar to the variation previously seen across all squamates or within long diverged snakes
Our finding of horizontal transposon transfer (HTT) into lineages of Hydrophiinae exposed to marine habitats’ environments, indicates that novel environments may play a large role in HTT through exposure to new TEs

Summary

Introduction

Variation is the fundamental basis of all evolutionary change, and mobile genetic elements are a major source of genomic variation. A high proportion of animal and plant genome sequences is derived from transposable elements (TE) and TEs are acknowledged drivers of evolutionary change, but their impacts are poorly understood. Understanding how TEs drive evolutionary change requires studying systems that are young, species-rich and ecologically diverse. In these respects, elapid snakes present excellent opportunities for the study of TE dynamics and their contribution to adaptive changes. Elapids are a diverse group of venomous snakes found across Africa, Asia, the Americas and Australia

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