Range eclipse leads to tenuous survival of a rare lizard species on a barrier atoll

Jonathan Q Richmond,Elijah Wostl,Robert N Reed,Robert N Fisher

doi:10.1017/s0030605320001404

Jonathan Q Richmond, Elijah Wostl + Show 2 more

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https://doi.org/10.1017/s0030605320001404

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Abstract

AbstractRediscovery of living populations of a species that was presumed to be extirpated can generate new narratives for conservation in areas suffering from losses in biodiversity. We used field observations and DNA sequence data to verify the rediscovery of the Critically Endangered scincid lizardEmoia slevinion Dåno′, an islet off the coast of Guam in the southern Mariana Islands, where for > 20 years it had been considered possibly extirpated. Endemic to the Marianas,E. slevinihas declined throughout its range and no longer occurs on as many as five islands from which it was historically known, most likely because of interactions with invasive species and loss of native forest. Our results show that individuals from Dåno′, the type locality forE. slevini, are genetically similar but not identical toE. slevinion Sarigan and Alamagan to the north, and thatE. sleviniis a close evolutionary relative to another congener in the southern Marianas that is currently recognized asEmoia atrocostatabut probably represents an undescribed species in this archipelago. We also show that other, more broadly distributed species ofEmoiaoccurring on Dåno′ are distant relatives toE. sleviniand the Mariana lineage ofE. atrocostata, providing further evidence of the distinctiveness of these taxa. The rediscovery ofE. slevinion Dåno′ following rodent eradication and culling of a population of monitor lizards suggests that management of invasive species is key to the recovery of this skink in the Mariana Islands, and that a range eclipse on the larger neighbouring island of Guam best explains why the rediscovery took place at the periphery of the species’ historic range. A Chamorro abstract can be found in the supplementary material.

Highlights

Rediscoveries of species once considered extinct or extirpated provide rare opportunities for positive messaging about biodiversity and add to a growing list of examples of successful management outcomes for indigenous species affected by non-indigenous invaders (Ladle et al, ; Jones et al, )
Rediscoveries may be likely for secretive taxa that occur in under-surveyed or remote areas (Scheffers et al, ; Caviedes-Solis et al, ), where habitat loss has resulted in scattered populations of a formerly widespread species (Fisher & Blomberg, ), where detection probabilities are low to begin with (Durso et al, ; Lee et al, ; Thompson et al, ; Butchart et al, ), and where invasive species may be suppressing the densities of individuals below thresholds of detectability but without causing extirpation or extinction (Morrison et al, )
All NADH gene (ND) sequences of E. slevini from Dåno′ were identical to each other but had unique substitutions compared to two haplotypes from Sarigan, one of which was identical to the single haplotype from Alamagan

Summary

Introduction

Rediscoveries of species once considered extinct or extirpated provide rare opportunities for positive messaging about biodiversity and add to a growing list of examples of successful management outcomes for indigenous species affected by non-indigenous invaders (Ladle et al, ; Jones et al, ). Among the numerous non-indigenous animals present on Guam, some of the most notorious and damaging are the brown treesnake Boiga irregularis, invasive rats Rattus spp., house mouse Mus musculus, marine toad Rhinella marina, musk shrew Suncus murinus, curious skink Carlia ailanpalai, coconut rhinoceros beetle Oryctes rhinoceros, and the little fire ant Wasmannia auropunctata (Fritts & Rodda, ; Raymundo & Miller, ; Marshall et al, ). These and other species have contributed to the dramatic decline, extirpation or extinction of Guam’s indigenous birds (Savidge, ), lizards (Rodda & Fritts, ) and mammals (Wiles, )

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