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Adaptive radiation is a significant driver of biodiversity. Primarily studied in animal systems, mechanisms that trigger adaptive radiations remain poorly understood in plants. A frequently claimed indicator of adaptive radiation in plants is growth form diversity when tied to the occupation of different habitats. However, it remains obscure whether morphological adaptations manifest as growth form diversity per se or as its constituent traits. We use the classic Aeonium radiation from the Canary Islands to ask whether adaptation across climatic space is structured by growth form evolution. Using morphological sampling with site-associated climate in a phylogenetic context, we find that growth forms dictate adaptations to the local environment. Furthermore, we demonstrate that the response of specific traits to analogous environments is antagonistic when growth forms are different. This finding suggests for the first time that growth forms represent particular ecological functions, allowing the co-occurrence of closely related species, being a product of divergent selection during evolution in sympatry.

Additional file 1. Additional figures S1–S6.

Background Wolbachia is an endosymbiont common to most invertebrates, which can have significant evolutionary implications for its host species by acting as a barrier to gene flow. Despite the importance of Wolbachia, still little is known about its prevalence and diversification pattern among closely related host species. Wolbachia strains may phylogenetically coevolve with their hosts, unless horizontal host-switches are particularly common. We address these issues in the genus Erebia, one of the most diverse Palearctic butterfly genera. Results We sequenced the Wolbachia genome from a strain infecting Erebia cassioides and showed that it belongs to the Wolbachia supergroup B, capable of infecting arthropods from different taxonomic orders. The prevalence of Wolbachia across 13 closely related Erebia host species based on extensive population-level genetic data revealed that multiple Wolbachia strains jointly infect all investigated taxa, but with varying prevalence. Finally, the phylogenetic relationships of Wolbachia strains are in some cases significantly associated to that of their hosts, especially among the most closely related Erebia species, demonstrating mixed evidence for phylogenetic coevolution. Conclusions Closely related host species can be infected by closely related Wolbachia strains, evidencing some phylogenetic coevolution, but the actual pattern of infection more often reflects historical or contemporary geographic proximity among host species. Multiple processes, including survival in distinct glacial refugia, recent host shifts in sympatry, and a loss of Wolbachia during postglacial range expansion seem to have jointly shaped the complex interactions between Wolbachia evolution and the diversification of its host among our studied Erebia species. Supplementary Information The online version contains supplementary material available at 10.1186/s12862-021-01822-9.

Phylogenies for the 16 genera studied in depth.

Output of the ChromoSSE models as supplementary figures ESM4.1 to ESM4.5

Summary of the Brownian Motion analysis

Premise of research. Self-compatibility is a requirement for reproductive assurance via selfing and may therefore be beneficial in environments with infrequent or unpredictable pollinator service. However, self-compatible plants may spatially separate anthers from stigmatic surface within flowers (herkogamy), potentially preventing autonomous self-pollination while promoting outcrossing. We investigated the effects of herkogamy on patterns of mating in a self-compatible, homostylous alpine herb, Primula halleri, which evolved from obligately outcrossing, heterostylous ancestors. Primula halleri displays diminishing herkogamy during anthesis, affecting its capacity for self-pollination. Specifically, we tested whether higher herkogamy at the end of anthesis (terminal herkogamy) promotes higher outcrossing rates at the cost of lower seed set, while lower terminal herkogamy ensures seed set via self-pollination at the cost of inbreeding. Methodology. We estimated family- and population-level genetic outcrossing rates in four populations using microsatellites and derived an estimate for inbreeding depression. We tested effects of different levels of terminal herkogamy on means and variances of outcrossing rates. We also assessed whether seed set was resource or pollen limited. We interpreted results in light of previously published data on seed set with and without pollinator-exclusion treatment. Pivotal results. Population-level outcrossing rates ranged between 0.5 and 0.8. Outcrossing rates of plants with higher terminal herkogamy had similar means but lower variances than those of plants with lower terminal herkogamy. This result demonstrates that separation between sexual organs larger than 1 mm in mature flowers favors outbreeding, while below this threshold, delayed selfing ensures reproduction. Conclusions. Contrary to long-held notions about the association of homostyly and selfing, we provide new genetic evidence that the homostylous P. halleri adopts a mixed mating system due to variable herkogamy. Moreover, our results support a trade-off between seed number and seed quality effected through variation in herkogamy, illustrating that herkogamy affects multiple aspects of reproductive fitness simultaneously.