Population Connectivity and Traces of Mitochondrial Introgression in New Zealand Black-Billed Gulls (Larus bulleri).

Claudia Mischler,Bruce Robertson,Tracey Van Stijn,Rudiger Brauning,Andrew Veale,John Mcewan,Richard Maloney

doi:10.3390/genes9110544

Claudia Mischler, Bruce Robertson + Show 5 more

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https://doi.org/10.3390/genes9110544

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Abstract

Black-billed gulls (Larus bulleri) are endemic to New Zealand and are suspected to be undergoing substantial population declines. They primarily breed on open gravel beds in braided rivers of the South Island—a habitat that is diminishing and becoming increasingly modified. Although management of this species is increasing, little has been published on their movements and demographics. In this study, both mitochondrial DNA (mtDNA) control region domain I and nuclear single nucleotide polymorphisms (SNPs) were examined to help understand the connectivity and population structure of black-billed gulls across the country and to help inform management decisions. Mitochondrial DNA showed no population structure, with high haplotype and low nucleotide diversity, and analyses highlighted mitochondrial introgression with the closely related red-billed gulls (Larus novaehollandiae scopulinus). Nuclear DNA analyses, however, identified two groups, with Rotorua birds in the North Island being distinct from the rest of New Zealand, and isolation-by-distance evident across the South Island populations. Gene flow primarily occurs between nearby colonies with a stepwise movement across the landscape. The importance from a genetic perspective of the more isolated North Island birds (1.6% of total population) needs to be further evaluated. From our results, we infer that the South Island black-billed gull management should focus on maintaining several populations within each region rather than focusing on single specific colonies or river catchments. Future study is needed to investigate the genetic structure of populations at the northern limit of the species’ range, and identify the mechanisms behind, and extent of, the hybridisation between red-billed and black-billed gulls.

Highlights

The dynamics of gene flow, dispersal, and the potential causes of population structuring are important to understand when creating a management plan for a species [1]
Since genetic studies of black-billed gulls have never been conducted, movements of birds are not well understood, and management of the species is increasing, here we assessed the patterns of population structure in black-billed gulls. Using both mitochondrial DNA (mtDNA) and nuclear DNA, we examined the genetic structure of this endemic species using samples from across its range in New Zealand
We examined the potential for gene flow among gull populations, which would be consistent with the observation of dispersal between river catchments and between the North and South islands of New Zealand [15,16,17,18]

Summary

Introduction

The dynamics of gene flow, dispersal, and the potential causes of population structuring are important to understand when creating a management plan for a species [1]. Genes 2018, 9, 544 variability within and between populations, and highlighting the ability of these groups to respond to declines over the long term [3,4,5]. Black-billed gulls/tarāpuka (Larus bulleri) are endemic to New Zealand and exist primarily in the. South Island [6], with only approximately 1.6% of the population inhabiting the North Island [7]. Island colonies appear to be a recent expansion, with the Rotorua breeding colony only establishing since the 1930s. Since 2012, the New Zealand Threat Classification System has listed the species as ‘Threatened, Nationally Critical’, due to suspected rapid population declines [8]. Birds along the southern end of the North Island are assumed to be from the South Island, and birds in the Firth of Thames of the North Island are assumed to be from Rotorua and Gisborne [13]

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