# Past Colony Connectivity of a Declining Seabird Derived From Host–Parasite Genetic Data

## TL;DR

This study uses genetic data from seabirds and their parasites to understand how black-legged kittiwake colonies are connected across the North Atlantic.

## Contribution

The study introduces a novel use of host–parasite genetic data and Bayesian analysis to infer past colony connectivity in a wide-ranging seabird.

## Key findings

- Kittiwake dispersal and summer breeding movements show a longitudinal east-to-west trend.
- Connectivity among colonies is less likely across the Atlantic Ocean.
- Geographic distance weakly constrains connectivity, with other factors like colony status playing a role.

## Abstract

The black‐legged kittiwake (
Rissa tridactyla
, hereafter ‘kittiwake’, conservation status ‘Vulnerable’) is a long‐lived, highly motile and wide‐ranging seabird. Breeding kittiwake colonies are abundant across the northern hemisphere. The kittiwake's life history and the spatial scale of its breeding distribution make understanding colony connectivity a challenge; current species management models kittiwake colonies as closed units. Here, we explored the use of Bayesian analysis of multilocus microsatellite genotypes in the program BayesAss (BA3) to infer dispersal and seasonal summer breeding movements (information‐gathering behaviour; prospecting) (collectively ‘connectivity’) of kittiwakes around the North Atlantic. This approach uses the concept of inheritance by descent (IBD) (the formulation of genotypes within a population mediated by inheritance) and Markov‐chain Monte Carlo (MCMC) resampling to quantify patterns of breeding movements among spatial aggregations of related individuals. Data comprised diploid microsatellites of the kittiwake and the common seabird tick (
Ixodes uriae
) sampled from the High Arctic to the lower southern boundary of the species between the years of 1992 and 2001. Kittiwake dispersal and summer breeding movements, the latter derived from tick microsatellites, were heterogenous among the sampled colonies. There was an east to west longitudinal trend in dispersal. Summer breeding movements were more localised, although still present at large spatial scales. Connectivity among kittiwake colonies was less likely across the Atlantic Ocean. This study supports the prevailing theory that geographic distance only weakly constrains connectivity among kittiwake colonies. Multimodal relationships between geographic distance and connectivity indicate that other factors, such as colony status and conspecific associations may be more important.

Species assessments currently define discrete black‐legged kittiwake colonies as closed populations; a precautionary approach potentially lacking in biological realism. Here, a past dataset of host–parasite multilocus microsatellite genotypes and a well‐established Bayesian inferential analytical programme, BayesAss (BA3), were used to estimate recent dispersal and seasonal summer breeding movements among kittiwake colonies (collectively, colony ‘connectivity’). Despite uncertainty around dispersal estimates inferred from kittiwake microsatellites, results were indicative of dispersal occurring over large geographic scales and predominantly longitudinally, east to west. Tick microsatellite analyses (a proxy of kittiwake movements during the summer breeding season) grouped colonies in Iceland, Norway, Scotland and France separately from Newfoundland and Barents Sea colonies. Non‐linear negative relationships between geographic distance and colony connectivity suggest that spatial scale may be an important, but not the only, mechanism underpinning dispersal and breeding movements in kittiwakes.