Claudia Ciotir

Landscape structure and the genetic effects of a population collapse.

Both landscape structure and population size fluctuations influence population genetics. While independent effects of these factors on genetic patterns and processes are well studied, a key challenge is to understand their interaction, as populations are simultaneously exposed to habitat fragmentation and climatic changes that increase variability in population size. In a population network of an alpine butterfly, abundance declined 60–100% in 2003 because of low over-winter survival. Across the network, mean microsatellite genetic diversity did not change. However, patch connectivity and local severity of the collapse interacted to determine allelic richness change within populations, indicating that patch connectivity can mediate genetic response to a demographic collapse. The collapse strongly affected spatial genetic structure, leading to a breakdown of isolation-by-distance and loss of landscape genetic pattern. Our study reveals important interactions between landscape structure and temporal demographic variability on the genetic diversity and genetic differentiation of populations. Projected future changes to both landscape and climate may lead to loss of genetic variability from the studied populations, and selection acting on adaptive variation will likely occur within the context of an increasing influence of genetic drift.

Cryptic intercontinental dispersal, commercial retailers, and the genetic diversity of native and non-native cattails (Typha spp.) in North America

Although cattails (Typha spp.) are important components of wetlands around the world, the three most widespread species (T. angustifolia, T. domingensis, T. latifolia) are becoming increasingly dominant. We used global phylogenetic and phylogeographic assessments to test the hypotheses that each species has experienced multiple introductions of divergent lineages into North America and that commercial retailers are aiding long-distance dispersal. Our analyses identified T. angustifolia as a paraphyletic species with a highly divergent lineage. We found evidence for at least one introduced T. angustifolia lineage in wild populations and garden centres of North America. Although potentially complicated by incomplete lineage sorting, our data suggest dispersal of T. domingensis between Europe and Australia, and further investigation should assess a possible introduction of a non-native T. domingensis lineage into North America. T. latifolia has experienced bidirectional dispersal between North America and Europe, and a sample of T. latifolia purchased in a Canadian garden centre was an Asian lineage. Interspecific hybridization and novel intraspecific admixture have been repeatedly implicated in biological invasions, including invasions by the hybrid cattail Typha × glauca, and future work should focus on the potential contributions of non-native lineages to regional patterns of invasion by Typha spp. in North America.

Widespread cytonuclear discordance in narrow-leaved cattail (Typha angustifolia) does not explain the dominance of its invasive hybrid (Typha × glauca)

Cattails (Typha spp.) are common and abundant in wetlands around the world, and can be invasive. Typha latifolia and T. angustifolia are two widely distributed species that in North America produce the invasive hybrid T. × glauca, of which T. angustifolia is the maternal parent. A recent study identified polyphyly in T. angustifolia resulting from core and divergent chloroplast DNA (cpDNA) lineages. We used a combination of chloroplast and nuclear genetic data to test two hypotheses: (1) T. angustifolia with the divergent cpDNA lineage represents a cryptic species and (2) divergent cpDNA T. angustifolia haplotypes predominate in areas where T. × glauca is invasive. Our data reject the hypothesis of a cryptic species, and we suggest that the divergent lineage arose in T. angustifolia following historical hybridization and introgression. Typha × glauca may therefore be a three-way hybrid involving T. latifolia, T. angustifolia, and an introgressed cpDNA lineage from an unidentified congener. The divergent cpDNA T. angustifolia haplotype is widespread across areas where T. × glauca is invasive, but is also found in areas where T. × glauca is maintained at very low frequencies; therefore, cpDNA lineages cannot be the sole explanation for T. × glauca invasiveness.