Genetic Connectivity of <scp> <i>Profilicollis altmani</i> </scp> in Seabirds: Effects of Host Trophic Ecology on Chilean Coasts

ABSTRACT Profilicollis altmani is an acanthocephalan parasite widely distributed along the Pacific and Atlantic coasts of the Americas, where gulls serve as its definitive hosts. This study investigates the genetic structure of P. altmani populations in relation to the life‐history traits of three sympatric gull species: Larus dominicanus , Chroicocephalus maculipennis and Leucophaeus modestus , along the Chilean coast. Mitochondrial (COI) and nuclear (28S) genetic markers were employed to assess patterns of genetic diversity, population structure, and connectivity. To evaluate the ecological drivers of parasite gene flow, host traits such as diet composition, foraging habitat, and migratory behaviour were analyzed alongside parasite genetic data. Molecular, phylogenetic and species delimitation analyses revealed a high degree of genetic connectivity among P. altmani populations, characterised by widespread haplotype sharing across host‐associated groups and low FST values, indicating substantial gene flow. Nevertheless, some host‐specific haplotypes were identified, which may reflect early stages of host‐associated genetic differentiation. A Random Forest model revealed that host migratory behaviour is a strong predictor of the observed genetic homogeneity in parasite populations. The results suggest that the high mobility of gull hosts, combined with overlapping habitat use and shared trophic resources, facilitates parasite transmission and limits genetic structuring among P. altmani populations. The absence of significant genetic divergence across host species and geographic regions underscores the influence of host ecology in shaping parasite population genetics. These findings highlight the value of integrating host life‐history traits to better understand genetic connectivity and evolutionary dynamics in generalist marine parasites, offering insight into how ecological interactions at the host level can drive patterns of genetic structure in parasitic systems.