Does Invading Change You?

The red lionfish, an aggressive, fecund, and competitive species invasive to the Atlantic Ocean (Image Credit: Alexander Vasenin, CC BY-SA 3.0).

The genomics of invasion: characterization of red lionfish (Pterois volitans) populations from the native and introduced ranges (2019) Burford Reiskind et al., Biological Invasions, https://doi.org/10.1007/s10530-019-01992-0(0123456789

The Crux

Invasive species are one of the most destructive forces and largest threats to native ecosystems, second only to habitat loss. The “how” and “when” of a species invading new habitats is obviously important, and as such many studies focus on if invasive species are present and if they are spreading. Yet these studies often disregard the mechanisms behind why a species is spreading or succeeding in these new environments. The mechanisms are important here, because by and large most invasive organisms will have very small populations sizes, leaving them vulnerable to stochastic events like environmental flux, disease, and inbreeding depression.

Two key paradoxes of invasive species are that these small groups of invasive organisms tend to not only have more genetic diversity than the native species (making them more adaptable to environmental change), but they are also able to outcompete the native organisms, despite having evolved in and adapted to what may be a completely different environment. The authors of this study used genomic approaches to address and try to understand these paradoxes. 

What They Did

The authors sampled red lionfish from both their native (2 locations) and invasive (5 locations) ranges, collecting multiple fish at each site. Using fin clippings from each fish, they collected info on genetic diversity, inbreeding, and genetic differentiation.

They wanted to understand the genetic structure of red lionfish populations both within the native and introduced ranges, and look into whether there are some parts of the genome under selection. Doing this would allow the authors to understand where the original source population of introduced red lionfish was, if and how the genetic structure varied in the invasive and native areas, and what (if any) genes and traits may be under selection in either the native or invasive habitats.

Did You Know: Founder Effects

A big issue for invasive or dispersing species is the so-called “founder effect”, where the invasive or dispersing population tends to be smaller and only include a subset of the original genetic makeup of the source population. When this happens, the new population may suffer from an increased occurrence of genetic abnormalities, due to their limited gene pool. As a result, small populations like those of invasive species (at least at the beginning of their invasion) are thought to not be able to survive for long.

What They Found

Surprisingly, the genetic diversity of the invasive populations did not differ from that of the native populations. Another surprising result was that the native populations were more inbred than the invasive ones, which would normally indicate that there were multiple waves of invasion, which subsequently mixed, avoiding inbreeding. However, the data goes directly against this idea, suggesting that there was a single invasion event, and the invasive population’s genetic diversity was created in their native area.

Another theory was that the genetic diversity of the invasive populations was due to hybridization (breeding with another species and forming a hybrid that may eventually become a species in its own right) with another closely-related lionfish species also found in the area. However this turned out not to be true, and the most likely explanation for the high diversity is the founder effect (see above).

Because of the large appetite of the lionfish and lack of predators in the invasive range, they easily outcompete native fish like this grouper (Image Credit: Kevin Bryant CC BY-NC-SA 2.0)

Problems

The majority of the fish sampled in the invasive range all came from the southern limits of the invasive lionfish. These fish have spread as far north as the New England coast of the United States, meaning that there could be other interesting genetic or ecological dynamics at play in this system, but it’s hard to know with the “limited” study design used here.

So What?

Using a variety of genetic methods, the authors were not only able to pinpoint the likely source population of the invasive lionfish, but they were also able to investigate regions of the genome under selection in the new environment. These data, while suggesting that fish in the invasive range are more aggressive than their counterparts in the local range, are key if we are to better understand species invasions and how to better manage them in the future.

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