Why do taxa differ in species richness? A multifactorial evolutionary view at species richness disparities in microgastropods
Evolution, Anthropology
Final Report Abstract
Causes for differences in species richness among phylogenetic clades are their origination time or, alternatively, the variation in diversification rates (speciation minus extinction), which is driven by extrinsic (e.g. habitat type, geographic distribution and species co-occurrence) and/or intrinsic (e.g. morphological features) factors. While previous studies have usually tested the influence of single factors on diversification rate, multifactorial analyses accounting the complex interaction of causing factors are still scarce. Hence, the main goal of this project was to test for drivers of species richness disparities using a taxonomically and ecologically diverse model taxon (the continental aquatic gastropod family Hydrobiidae) and a novel multifactorial approach that enables estimation of the joint effect of these factors in a phylogenetic framework. Better knowledge on family-richness improves diversification rate estimations. Therefore, we assessed the hitherto unknown global diversity and geographic distribution of Hydrobiidae sensu stricto with a literature survey and counted a total of 906 extant species classified in 157 genera. We also inferred priority areas for conservation (i.e. biodiversity hotspots), found that extinction risk peaks at mid-elevations and coded latitude, connectivity, biogeographical realm, precipitation seasonality and annual temperature range as predictors of species richness patterns. Samples obtained from field work and external collaborators yielded a genetic dataset based on two mitochondrial and two nuclear gene fragments of >400 hydrobiid species, covering ca. 50% of the family’s richness. A Bayesian species tree and Bayesian macroevolutionary modeling showed differences in diversification rates among hydrobiid clades. We first inferred the drivers of diversification in two closely-related clades, displaying different rates, as pilot study for the potentially complex diversification history of the whole family. Our analyses evidenced that Pseudamnicola, a species-rich genus occurring mostly in lowland waters, showed significantly increased speciation rates in comparison to the species-poor ‘headwater genus’ Corrosella. State-dependent speciation models showed that the speciation rate increased with decreasing elevation. The integration of phylogenetic data with morphological and habitat traits supported the hypothesis that lowland lineages experienced higher ecological opportunity through dispersal to new locations, more likely in lowlands due to higher connectivity and presence of dispersal vectors such as fish or birds. This first stimulated diversification and later morphological disparification. One major point of criticism during the peer review of the Pseudamnicola/Corrosella study was the inclusion of undescribed lineages (under the provisional name “sp.”) in the phylogenetic tree. The inferred Hydrobiidae species tree revealed 50 lineages that represent species new to science. The inclusion of these newly discovered taxa in the diversification analyses is crucial for a more complete taxon sampling. To avoid the same criticism, we first needed to formally describe them based on the integration of morphological and genetic evidence before proceeding with the planned objectives. In parallel, we inferred the biogeographical history of selected groups. We discovered trans-Mediterranean and trans-Arctic dispersal routes at 3–1 Mya, probably mediated by birds and rarely found in other freshwater taxa; playing a key role for their diversification. First diversification analysis based on the ca. 50% of the family’s richness showed an influence of habitat type on diversification, with species living in subterranean and lacustrine habitats evolving more rapid than those from springs, rivers and brackish waters. This analysis also indicated habitat-independent changes in diversification rate, potentially caused by other species’ traits. We are currently implementing the multifactorial path analysis of the relative influence of several factors (e.g. habitat, body size and species competition), which we proposed in the project application. In parallel, we published a novel analysis demonstrating how habitat change affects the rate of evolutionary diversity build-up in freshwater ecosystems.
Publications
- (2017). A new genus and species of uncertain phylogenetic position within the family Hydrobiidae (Caenogastropoda, Truncatelloidea) discovered in Tunisian springs. European Journal of Taxonomy 328, 1–15
Khalloufi, N., Béjaoui, M. & Delicado, D.
(See online at https://doi.org/10.5852/ejt.2017.328) - (2018). Ecological opportunity may facilitate diversification in Palearctic freshwater organisms: a case study on hydrobiid gastropods. BMC Evolutionary Biology 18, 55
Delicado, D., Hauffe, T. & Wilke, T.
(See online at https://doi.org/10.1186/s12862-018-1169-2) - (2018). The genus Mercuria Boeters, 1971 in Morocco: first molecular phylogeny of the genus and description of two new species (Caenogastropoda, Truncatelloidea, Hydrobiidae). ZooKeys 782, 95–128
Boulaassafer, K., Ghamizi, M. & Delicado, D.
(See online at https://doi.org/10.3897/zookeys.782.26797) - (2019). Hydrobiidae Stimpson, 1865. In: Freshwater mollusks of the world: a distribution atlas. Charles Lydeard & Kevin S. Cummings (eds). Johns Hopkins University Press, Baltimore, U.S.A.
Wilke, T. & Delicado, D.
- (2019). Multilocus phylogeny, species delimitation and biogeography of Iberian valvatiform springsnails (Caenogastropoda: Hydrobiidae), with the description of a new genus. Zoological Journal of the Linnean Society 186, 892–914
Delicado, D., Arconada, B., Aguado, A. & Ramos, M.A.
(See online at https://doi.org/10.1093/zoolinnean/zly093) - (2020). Lake expansion elevates equilibrium diversity via increasing colonization. Journal of Biogeography
Hauffe, T., Delicado, D., Etienne, R.S. & Valente, L.
(See online at https://doi.org/10.1111/jbi.13914) - (2020). Phylogenetic relationships within Pseudamnicola Paulucci, 1878 (Caenogastropoda: Truncatelloidea) indicate two independent dispersal events from different continents to the Balearic Islands. Systematics and Biodiversity 18(4), 396–416
Boulaassafer, K., Ghamizi, M., Machordom, A. & Delicado, D.
(See online at https://doi.org/10.1080/14772000.2020.1771466)
