Reproduction ecology of the recently invasive snake Hemorrhois hippocrepis on the island of Ibiza

Abstract

Knowing the causes of biological invasion success can be relevant to combat future invasive processes. The recent invasion of the horseshoe whip snake Hemorrhois hippocrepis on the island of Ibiza provides the opportunity to compare natural history traits between invasive and source populations, and to unravel what makes this snake a successful invader that is threatening the only endemic vertebrate of the island, Podarcis pityusensis. This study compares the basic reproductive traits of mainland native and invasive populations of the snake. Our results revealed that invasive populations were characterized by female maturity at a smaller size, extended reproductive period, and much lower reproduction frequency compared to the native population. In contrast, some major reproductive traits—the abdominal fat body cycle, clutch size, hatchling body size, and hatchling body condition, did not differ between the two populations. Some of these results must reflect the environmental differences in the recently invaded island with respect to the source area, and overall plasticity of reproductive traits. Plasticity is evolutionarily interesting, and may aid the successful growth of this species in their invasiveness of Mediterranean islands like Ibiza. The most significant finding is that this expression of phenotypic plasticity occurred rapidly in this invasive population, within a period of 14 years maximum. Our results on the reproduction ecology of the invasive population were not conclusive regarding the factors determining the invasiveness of the snake and pointed to alternative causes.

The Horseshoe whip snake (Hemorrhois hippocrepis) on Ibiza: predator release in an invasive population

“…The invasive population of H. hippocrepis on Ibiza is exhibiting a fast process of phenotypic plasticity; in only 13 years, some island individuals have become larger (105% of body length and 213% of body weight) than individuals from the source population (Montes et al, 2015). However, the study of its feeding and reproduction ecology failed in supporting the extraordinary body condition of individuals and the invasiveness of the population (see also Hinckley et al, 2017 andMontes et al, 2019). Thus, we suggest that their success may be favored by one of the environmental conditions of Ibiza, that is the low predation pressure on H. hippocrepis on this island (Hinkley et al, 2017), given that most of its predators in the source area are absent on the invaded island.…”

“…Furthermore, the trophic and reproduction ecology of H. hippocrepis failed to explain the success of that invasive population on Ibiza; the low rate of feeding frequency (20.8% were fed individuals) and the small size for the main prey (a small lizard, 4 g of body weight on average), poorly supports the high body condition of alien individuals (Hinckley et al, 2017); and their much lower female reproduction frequency compared to the native population (biennial vs annual) was not conclusive in determining the invasiveness of the snake (Montes et al, 2019).…”

Reproductive plasticity as an advantage of snakes during island invasion

“…Increased allelic diversity due to multiple introductions from the pet trade may further help to explain the differences in the Canary Island and native snakes' reproductive biology (Card et al, 2018;Montes, Feriche, Ruiz-Sueiro, Alaminos, & Pleguezuelos, 2020;Nania, Flecks, & Rodder, 2020). It is possible that L. californiae in the invasive population may have a heterozygosity advantage that results from range-wide genetic diversity (Monz on-Argüello et al, 2015), resulting in more reproductive plasticity than if they had come from one singular native locality (Ji & Wang, 2005).…”

Demographic monitoring of the invasive ladder snake on Formentera (Balearic Islands, Spain)

“…Demographic analyses of wild populations involve assessing basic ecological parameters (Brown & Weatherhead, 1999; Jordan & Rodda, 1994; Montes, Feriche, et al., 2021; Park, 2004; Pleguezuelos et al., 2007) that are essential to understand the biology, trophic ecology, and reproductive traits of a species (Aldridge & Brown, 1995; Caughley, 1994; Ford & Seigel, 1989; Gibbons, 1972; Godley, 1980; Rose et al., 2013). Snakes' nocturnality, broad movements, low recapture rates, crypsis, and periods of inactivity (Durso & Seigel, 2015; Steen, 2010; Ward et al., 2017) may have prevented the study of their demography in the past.…”