Phylogeography of Bornean land snails suggests long‐distance dispersal as a cause of endemism

Abstract

Aim Islands are often hotspots of endemism due to their isolation, making colonization a rare event and hence facilitating allopatric speciation. Dispersal usually occurs between nearby locations according to a stepping‐stone model. We aimed to reconstruct colonization and speciation processes in an endemic‐rich system of land‐based islands that does not seem to follow the obvious stepping‐stone model of dispersal. Location Five land‐based habitat archipelagos of limestone outcrops in the floodplain of the Kinabatangan River in Sabah, Malaysian Borneo. Methods We studied the phylogeography of three species complexes of endemic land snails, using multiple genetic markers. We calculated genetic distances between populations, applied beast2 to reconstruct phylogenies for each taxon and subsequently reconstructed ancestral ranges using ‘BioGeoBEARS’. Results We found spatial‐genetic structure among nearby locations to be highly pronounced for each taxon. Genetic correlation was present at small spatial scales only and disappeared at distances of 5 km and above. Most archipelagos have been colonized from within the region multiple times over the past three million years, in 78% of the cases as a result of long‐distance dispersal (LDD) or dispersal from non‐adjacent limestone outcrops. The flow of the main geographical feature within the region, the Kinabatangan River, did not play a role. Main conclusions Phylogeographic structure in these Bornean land snails has only partly been determined by small‐scale dispersal, where it leads to isolation‐by‐distance, but mostly by LDD. Our results demonstrate that island endemic taxa only very locally follow a simple stepping‐stone model, whilst dispersal to non‐adjacent islands and especially LDD, is most important. This leads to the formation of highly localized, isolated “endemic populations” forming the onset of a complex radiation of endemic species.

Microbiome and environment explain the absence of correlations between consumers and their diet in Bornean microsnails

“…However, consumer community and individual diet diversities do not increase with decreasing distance to the next habitat island (should this be taken as a proxy for “the mainland” from the equilibrium theory). This is in line with recent work by Hendriks et al (2019 a ), who showed little effect of distance on the colonization opportunities in these snail consumers communities. Third, community diversities are lower close to cave entrances, which might be a result of the local eutrophic conditions caused by runoff from bat and swiftlet guano.…”

“…We studied species‐rich consumer communities of land snails, their seed plant diets, and microbiomes, in the Lower Kinabatangan Floodplain in Sabah, Malaysian Borneo (Schilthuizen et al 2003, Schilthuizen 2011, Hendriks et al 2019 a , b ). Most snail community members have a preference for calcium carbonate as a substratum or depend on it.…”

“…Given the usually close relationship between consumers and their resources, we aimed to answer the question of how consumers’ individual diets are influenced by the community in which these individuals live, in the light of a third community, the individual’s microbiome. To this end, we studied communities of land snails (Gastropoda) living in an archipelago‐like environment of habitat islands of limestone bedrock in lowland tropical rainforest in Sabah, Malaysian Borneo (Schilthuizen et al 2003, Schilthuizen 2011, Hendriks et al 2019 a , b ). We used a combination of snail consumer community census data and metabarcoding data from seed plant and bacterial genetic markers obtained from individual snail guts to reconstruct snail community, seed plant diet, and microbiome richness and diversity, and to study relationships between communities.…”

Biogeography, Systematics, and Ecomorphology of Pacific Island Anoles

“…As a result, islands have served as model systems for examining evolutionary processes like community assembly and speciation. Particularly in taxonomic groups with reduced lability, an island-mainland divide can promote allopatric speciation, leading to island endemism [4][5][6]. Many archipelagos that have featured prominently in the annals of evolutionary biology are of volcanic origin (e.g., the Canary, Galápagos, and Hawaiian Islands), where the nature of their formation necessitates any inhabitants to have almost certainly arrived via overwater dispersal [7], but the process of community assembly on continental islands can be different.…”

Insights into the evolutionary and demographic history of the extant endemic rodents of the Galápagos Islands

“…The goal of the present study was to undertake the first study including comprehensive sampling of all four extant endemic rodent terns of evolution due to their geographic isolation, small size, fewer numbers of species, and a high degree of endemism. The development of ecological and evolutionary systems can be directly observed on volcanic islands as we are now better able to date the timing of their emergence above the ocean surface as blank slates for colonization and the timing of subsequent evolutionary diversification (Losos and Ricklefs 2009;Hendriks et al 2019).…”