DOI: 10.5061/dryad.6djh9w147
title: Near-shore island lizard fauna shaped by a combination of human-mediated and natural dispersal

description: Aim: Island biotas provide opportunities to study colonization and
 adaptation to novel environments. Islands, especially near-shore islands,
 may have a long record of human habitation such that some lineages result
 from human-assisted introductions. Here, we combine phylogenetic analyses
 with fossil data and historical specimen records to reconstruct
 colonization histories, characterize among-island divergence, and assess
 the role of humans in shaping the evolutionary history of lizards
 inhabiting a near-shore island archipelago. Location: Channel Islands and
 adjacent mainland of California, USA. Taxa: Western fence lizard (
 Sceloporus occidentalis), southern alligator lizard (Elgaria
 multicarinata), common side-blotched lizard (Uta stansburiana). Methods:
 We sequenced mitochondrial DNA (ND1, cyt-b) from each of three lizard
 species, covering their entire island distributions plus the adjacent
 mainland. For each, we estimated diversity within and among each island,
 obtained maximum likelihood bootstrapped phylogenies, constructed
 haplotype networks, and tested for population expansion. We used museum
 specimen records and microfossil evidence to infer colonization scenarios.
 Results: Sceloporus occidentalis is characterized by a single
 island-colonization event, and exhibits the deepest divergences from
 mainland relatives and the highest among-island divergence. Elgaria
 multicarinata and Uta stansburiana each have at least three distinct
 colonization events, with fossil and historical data indicating that some
 of these occurred after humans arrived to the islands. Main Conclusions:
 The evolution of Channel Island lineages for two lizard taxa has been
 mediated by ancient and contemporary anthropogenic activity, while the
 evolution of the third is shaped by natural dispersal and vicariance
 caused by sea-level rise. Genetic divergence corroborates the treatment of
 S. occidentalis as an endemic island species, S. becki. The unique
 histories of these three taxa are synthesized with other Channel Island
 lineages highlighting that taxa inhabiting islands with long histories of
 human activity should be carefully studied to assess the role of people in
 facilitating colonization and subsequent gene flow. 
description: We examined the first date of known
 occurrence of each species on each island using museum collection records.
 Specimen occurrence data were downloaded from VertNet for <em>S.
 occidentalis, E. multicarinata, U. stansburiana, </em>and
 additionally for <em>Xantusia </em>and<em>
 Plestiodon/Eumeces</em>. We included these non-focal lizard species
 to assess overall lizard survey and collection efforts on each of the
 islands over time. In addition to the genus, we included the search terms
 “locality:(Island OR isla OR is.) stateprovince:(California NOT Baja).”
 Resulting records were checked manually, deleting records not from the
 Channel Islands and contacting museums to verify all outlier
 records. 
description: For the verified dataset, we visualized the number of records for
 each species in each collection year in R (R Core Team, 2022) using the
 packages DPLYR 1.0.8 (Wickham et al., 2022), GGPLOT2 3.3.5 (Wickham,
 2016), and RCOLORBREWER 1.1-3 (Neuwirth, 2022).