Drivers of predatory behavior and extreme size in house mice Mus musculus on Gough Island

Abstract

In comparison to the mainland, populations of rodents on islands are often characterized by a suite of life history characteristics termed the “island syndrome.” Populations of rodents introduced to islands are also well known for their impacts on native species that have evolved in the absence of mammalian predators. We studied the ecology and behavior of introduced house mice Mus musculus on Gough Island where they are the only terrestrial mammal and where their predatory behavior is having a devastating impact on the island’s burrowing petrel (order Procellariiformes ) population and the Critically Endangered Tristan albatross Diomedea dabbenena . Mice on Gough exhibit extreme features of the island syndrome, including: a body mass 50–60% greater than any other island mouse population, peak densities among the highest recorded for island populations, and low seasonal variation in numbers compared to other studied islands. Seasonal patterns of breeding and survival were linked to body condition and mass, and mice in areas with high chick predation rates were able to maintain higher mass and condition during the winter when mouse mortality rates peak. Within-site patterns of chick predation indicate that proximity to neighboring predated nests and nesting densities are important factors in determining the likelihood of predation. We conclude that selection for extreme body mass and predatory behavior of mice result from enhanced overwinter survival. Small mammal populations at temperate and high latitudes are normally limited by high mortality during the winter, but on Gough Island mice avoid that by exploiting the island’s abundant seabird chicks.

Genetics of Skeletal Evolution in Unusually Large Mice from Gough Island

“…The finding that QTL alleles from GI mice increase skeletal size in almost all cases suggests that natural selection targeted the skeleton or a correlated trait (Orr 1998). Body weight and body condition of GI mice correlate with overwinter survival, and mice that prey upon nestling seabird chicks maintain higher body weights during the winter season (Cuthbert et al 2016). These patterns raise the prospect that natural selection targeted overall body size in GI mice, driving substantial and rapid evolution of the skeleton.…”

“…Presence-absence or meristic polymorphisms of bones in the skull, humerus, pelvis, and vertebrae (including the tail) have been documented (Berry 1964(Berry , 1986Berry and Jakobson 1975a;Berry et al 1978;Davis 1983;Pergams and Ashley 2001;Renaud and Auffray 2010). Divergence in body size (Berry and Jakobson 1975b;Berry et al 1978bBerry et al , 1979Berry et al , 1981Berry et al , 1987Rowe-Rowe and Crafford 1992;Adler and Levins 1994;Jones et al 2003;Lomolino 2005;Roth 2012, 2015;Russell 2012;Gray et al 2015;Cuthbert et al 2016) suggests evolutionary changes to the skeleton in other island populations. As the scaffold for the body plan, the skeleton enables movement, provides support for muscles, and protects internal organs (Pourquié 2009).…”

Changing invaders: trends of gigantism in insular introduced rats

“…The world's largest feral house mice (almost twice the ancestral size; S i = 1.89) are found on Gough Island in the South Atlantic (Rowe-Rowe & Crafford 1992). This impressive body size increase is entirely due to a switch to a higher degree of carnivory, whereby the mice eat live seabird chicks (Gray et al 2014;Cuthbert et al 2016). The body size increase of the Polynesian rat is, however, even more impressive: slightly more than twice the ancestral size.…”

Masticatory Apparatus Performance and Functional Morphology in the Extremely Large Mice from Gough Island

“…Based on the strength of the size signal observed here, we hypothesize that the majority of masticatory apparatus changes may be primarily size‐correlated rather than driven by the functional requirements of a carnivorous diet (see below also). Cuthbert et al () similarly hypothesize that extreme body size and behavioral shifts to carnivory helped GI mice adapt to extreme winter conditions with limited alternative food resources.…”

“…House mice ( Mus musculus ) arrived on Gough Island (GI), remotely located near the center of the South Atlantic Ocean, approximately 100–200 years ago after being transported from the mainland by seafaring vessels (Rowe‐Rowe and Crafford, ; Jones et al, ; Gray et al, , ). Since their arrival, these mice rapidly evolved to weigh as much as twice that of their mainland relatives (Jones et al, ; Gray et al, ), making them the largest wild house mice on record (Rowe‐Rowe and Crafford, ; Gray et al, ; Cuthbert et al, ) (Fig. ).…”