Climatic niche pre-adaptation facilitated island colonization followed by budding speciation in the Madeiran ivy (Hedera maderensis, Araliaceae)

Climatic and edaphic niche shifts during plant radiation in the Mediterranean biodiversity hotspot

BACKGROUND AND AIMS

Ecological speciation is frequently invoked as a driver of plant radiation, but the behaviour of environmental niches during radiation is contentious, with patterns ranging from niche conservatism to niche divergence. Here, we investigated climatic and edaphic niche shifts during radiation in a western Mediterranean lineage of the genus Linaria (Plantaginaceae).

METHODS

Detailed distributional, phylogenomic and environmental data were integrated to analyse changes in climatic and edaphic niches in a spatiotemporal context, including calculation of niche overlap, niche equivalency and similarity tests, maximum entropy modelling, phylogenetic comparative methods and biogeographical analyses.

KEY RESULTS

Active divergence of climatic and edaphic niches within a limited subset of available conditions was detected among the eight study species and particularly between sister species. Speciation and niche divergence are estimated to have happened in the southern Iberian Peninsula in Mediterranean conditions, followed by waxing and waning of distribution ranges resulting from the Quaternary climatic cycles.

CONCLUSIONS

The results support the idea that the prevalence of niche conservatism or niche divergence patterns is a matter of phylogenetic scale. Habitat isolation pertaining to both climatic and soil conditions appears to have played a role in plant speciation in the western Mediterranean biodiversity hotspot, most probably in combination with pollinator isolation and some degree of geographical isolation. These findings are in agreement with an adaptive radiation scenario incorporating certain non-adaptive features.

Plant Neighbourhood as Predictor of Allopatric Speciation in Sedges

Adaptation to different environments in geographically separated populations is key for allopatric speciation. Most research has focused on the effects of geographical isolation and abiotic factors, but disjunct populations frequently co-occur with different pools of species, favouring divergent adaptation and speciation. We show the importance of plant neighbourhood, compared to geographic and environmental factors, in the allopatric speciation of two closely related plants, Carex elata and Carex reuteriana. Both species share similar ecological requirements and inhabit river shores at medium to low altitudes across the Iberian Peninsula. We employed a multidisciplinary approach integrating abiotic, biotic and geographical factors, and genomic data (genotyping-by-sequencing) to infer the relative role of different evolutionary drivers. Abiotic factors were assessed based on 38 bioclimatic variables, biotic factors using the community of co-occurring plant species (1536 vegetation inventories), and geographical factors with a distance matrix based on geographic coordinates. Using regularised generalised linear models, we identified the key variables explaining distribution patterns. We also examined the relationships between inter-population genetic distances, and biotic, abiotic and geographic factors to understand the drivers of lineage splitting, revealing varying degrees of influence. Plant neighbourhood emerged as a stronger predictor of allopatric distributions than abiotic or geographic factors, with the largest effect observed in Carex elata, which exhibited the greatest population differentiation. These findings suggest that the biotic and microenvironmental factors influencing divergent plant neighbourhoods have significantly contributed to the differentiation of these taxa, providing new insights into the evolutionary processes shaping the origin and distribution of species.

Unveiling the diversification and dispersal of the Lewinskya firma complex (Orthotrichaceae, Bryophyta) across Africa and India

Intercontinental disjunctions are one of the most attractive and interesting biogeographical patterns. Bryophytes often exhibit such distributions, which is partly explained by their great ability to disperse over long distances. However, such intercontinental ranges are sometimes a distorted reality caused by the existence of unnoticed species. This study investigates whether the disjunction between East Africa and southern India of the moss Lewinskya firma reflects the genuine distribution of a single species or implies pseudo-cryptic species (whose morphological differentiation is subtle and have therefore been masked). An integrative taxonomic approach combining morphological and molecular methods (genotyping by sequencing, GBS) was used, based on a representation of samples specifically collected from all the major mountainous regions where this moss occurs. Two species, L. firma s. str. and L. afroindica sp. nov. are involved, whose ranges completely overlap in East Africa, although genetic distance and morphological differences in leaf apex shape, vaginula hairs shape and papillosity, spore ornamentation and peristome constitution and ornamentation allow distinguishing both. In addition, the range of L. afroindica extends into both southern Africa and southern India. The phylogenetic reconstruction obtained shows a certain degree of differentiation of the Indian populations, although they are yet morphologically indistinguishable from African populations. The results thus highlight both the existence of overlooked species and the complexity of bryophyte biogeography.

High rate of species misidentification reduces the taxonomic certainty of European biodiversity databases of ivies (Hedera L.)

The digitization of natural history specimens and the popularization of citizen science are creating an unprecedented availability of large amounts of biodiversity data. These biodiversity inventories can be severely affected by species misidentification, a source of taxonomic uncertainty that is rarely acknowledged in biodiversity data management. For these reasons, taxonomists debate the use of online repositories to address biological questions at the species level. Hedera L. (ivies) provides an excellent case study as it is well represented in both herbaria and online repositories with thousands of records likely to be affected by high taxonomic uncertainty. We analyze the sources and extent of taxonomic errors in the identification of the European ivy species by reviewing herbarium specimens and find a high misidentification rate (18% on average), which varies between species (maximized in H. hibernica: 55%; H. azorica: 48%; H. iberica: 36%) and regions (maximized in the UK: 38% and Spain: 27%). We find a systematic misidentification of all European ivies with H. helix behind the high misidentification rates in herbaria and warn of even higher rates in online records. We compile a spatial database to overcome the large discrepancies we observed in species distributions between online and morphologically reviewed records.