An Evolutionary Portrait of the Brown Anole’s Invasion Biology

In a recent study in the Proceedings of the National Academy of Sciences, Bock et al. (2021) conduct a genomic and phenotypic appraisal of adaptive evolution and invasion biology of Anolis sagrei (Wikimedia Commons).

In 2004, Jason Kolbe and colleagues published a now-classic invasion biology study in Nature, mapping out the population genetics of invasive Anolis sagrei populations. Using approximately 1,200 bp of mtDNA sequence data (ND2 and adjacent tRNAs), Kolbe et al. examined the evolutionary origins of the Brown Anole in its journey out of its ancestral area (Cuba), and into a broad invasive range. In several out-of-Cuba dispersal events that formed the collective invasive Brown Anole in Florida, Kolbe et al. (2004) found that invasion had actually increased genetic diversity within these populations, far greater than that observed in the native range. Furthermore, many of the global invasive populations of A. sagrei (e.g., Taiwan, Grenada), sourced from Florida, had maintained comparably high levels of genetic diversity. Hence, the work by Kolbe et al. demonstrated that the repeated introduction of multiple, evolutionarily diverse lineages derived from the native range and subsequently injected into a novel range may be a key force in driving successful invasion.

If we fast-forward five years to 2009, two years prior to the release of the A. carolinensis genome, Chris Schneider publishes a paper in Integrative and Comparative Biology (Schneider 2009) titled “Exploiting genomic resources in studies of speciation and adaptive radiation of lizards in the genus Anolis.” In his paper, Schneider discusses the unique opportunity that lies ahead in understanding evolutionary theory through the lens of Anolis genomic resources. Schneider’s vision—as I perceive it—was one that sought to excite the evolutionary ecology community about the wonderful opportunities ahead that Anolis lizards present in understanding, most broadly, the genetic basis of adaptation.

Now, in 2021, more than 15 years after the study by Kolbe et al., Bock et al. (2021) return for an integrative evolutionary investigation of A. sagrei throughout Florida using a recently generated reference genome and corresponding morphological data. In line with Schneider’s (2009) perspective, Bock et al. (2021) tell a captivating story of adaptation, genome biology, and invasion. Wielding the power of one of the most contiguous and complete squamate genomes assembled to date (more on that another time!), the authors identified a large-effect locus posited to be responsible for adaptive shifts in limb length, which in turn provides insight into how natural selection can modulate hybridization during the course of biological invasion.

New literature alert!

Changes in selection pressure can facilitate hybridization during biological invasion in a Cuban lizard

In PNAS

Bock, Baeckens, Pita-Aquino, Chejanovski, Michaelides, Muralidhar, Lapiedra, Park, Menke, Geneva, Losos, and Kolbe

Abstract

Hybridization is among the evolutionary mechanisms most frequently hypothesized to drive the success of invasive species, in part because hybrids are common in invasive populations. One explanation for this pattern is that biological invasions coincide with a change in selection pressures that limit hybridization in the native range. To investigate this possibility, we studied the introduction of the brown anole (Anolis sagrei) in the southeastern United States. We find that native populations are highly genetically structured. In contrast, all invasive populations show evidence of hybridization among native-range lineages. Temporal sampling in the invasive range spanning 15 y showed that invasive genetic structure has stabilized, indicating that large-scale contemporary gene flow is limited among invasive populations and that hybrid ancestry is maintained. Additionally, our results are consistent with hybrid persistence in invasive populations resulting from changes in natural selection that occurred during invasion. Specifically, we identify a large-effect X chromosome locus associated with variation in limb length, a well-known adaptive trait in anoles, and show that this locus is often under selection in the native range, but rarely so in the invasive range. Moreover, we find that the effect size of alleles at this locus on limb length is much reduced in hybrids among divergent lineages, consistent with epistatic interactions. Thus, in the native range, epistasis manifested in hybrids can strengthen extrinsic postmating isolation. Together, our findings show how a change in natural selection can contribute to an increase in hybridization in invasive populations.

Literature cited:

Kolbe, J. J., Glor, R. E., Schettino, L. R., Lara, A. C., Larson, A., & Losos, J. B. 2004. Genetic variation increases during biological invasion by a Cuban lizard. Nature 431(7005): 177-181.

Schneider, C. J. 2008. Exploiting genomic resources in studies of speciation and adaptive radiation of lizards in the genus Anolis. Integrative and Comparative Biology 48(4): 520-526.