Persististrombus coronatus (Mollusca: Strombidae) in the lower Pliocene of Santa Maria Island (Azores, NE Atlantic): Paleoecology, paleoclimatology and paleobiogeographic implications
Abstract:The family Strombidae is one of the twenty-three families and subfamilies of gastropods associated with tropical environmental conditions, and therefore useful as a biogeographical and palaeoclimatic proxy. Today, the strombid genus Persististrombus is represented in the NE Atlantic by a single species restricted to the tropical Mauritanian-Senegalese Province. This work reports the occurrence of Persististrombus coronatus from the lower Pliocene of Santa Maria Island in the Azores Archipelago. Based on this o… Show more
“…However, we think that the beginning of the divergence of this species occurred before or during the dispersal events since the Africa to the Azores. Although the ages of the Azores islands are more recent than previously thought spanning from Santa Maria (4.1 Mya) to Pico (0.27 Mya) (Ávila et al., ; Sibrant, Hildenbrand, Marques, & Costa, ), our haplotype network indicates that the oldest haplotypes are in the central group, namely in São Jorge (1.32 Mya), which might have been first colonized by an A. vidalii ancestor.…”
Macaronesia has long been recognized as a natural model for studying evolutionary processes in plant diversification. Several studies have attempted to focus on single lineages, and few have covered the diversification of a family across all the archipelagos. We used a comprehensive sample to clarify the phylogenetic relationships and the biogeographic history of the Macaronesian Campanulaceae. Hypotheses related to the colonization of these archipelagos will be used to examine the diversification patterns of different lineages. We sequenced the ITS region and six cpDNA markers (atpB, matK, petD, rbcL, trnL‐F, and psbA‐trnH) from 10 Campanulaceae species, including seven endemic species in Macaronesia. The phylogeny of these taxa was reconstructed using maximum parsimony, maximum likelihood, and Bayesian inference. To study the relationships within each lineage, haplotype networks were calculated using NeighborNet and TCS algorithms. Moreover, data were combined with fossil information to construct time‐calibrated trees for the Macaronesian Campanulaceae species. The phylogenetic analyses are largely congruent with current taxon circumscriptions, and all the endemic genera formed monophyletic clades, namely Azorina in Azores; Musschia in Madeira; and Campanula in Cape Verde. The Azorina clade and the Cape Verde endemic Campanula may share a common ancestor in North Africa, and the divergence was dated ca. 12.3 million years ago (Mya). The divergence of the Musschia clade began in the Pliocene ca. 3.4 Mya. Moreover, several examples of intraspecific variation were revealed among the native species with a clear geographic structured patterns, suggesting that cryptic diversity might exist within the native Macaronesian Campanulaceae when compared to the close mainland taxa (e.g., Campanula erinus, Trachelium caeruleum), but additional studies are needed to support the molecular data. This study highlights the power of combining data (e.g., phylogeny and divergence times, with species distribution data) for testing diversification hypotheses within the unique Macaronesian flora, providing useful information for future conservation efforts.
“…However, we think that the beginning of the divergence of this species occurred before or during the dispersal events since the Africa to the Azores. Although the ages of the Azores islands are more recent than previously thought spanning from Santa Maria (4.1 Mya) to Pico (0.27 Mya) (Ávila et al., ; Sibrant, Hildenbrand, Marques, & Costa, ), our haplotype network indicates that the oldest haplotypes are in the central group, namely in São Jorge (1.32 Mya), which might have been first colonized by an A. vidalii ancestor.…”
Macaronesia has long been recognized as a natural model for studying evolutionary processes in plant diversification. Several studies have attempted to focus on single lineages, and few have covered the diversification of a family across all the archipelagos. We used a comprehensive sample to clarify the phylogenetic relationships and the biogeographic history of the Macaronesian Campanulaceae. Hypotheses related to the colonization of these archipelagos will be used to examine the diversification patterns of different lineages. We sequenced the ITS region and six cpDNA markers (atpB, matK, petD, rbcL, trnL‐F, and psbA‐trnH) from 10 Campanulaceae species, including seven endemic species in Macaronesia. The phylogeny of these taxa was reconstructed using maximum parsimony, maximum likelihood, and Bayesian inference. To study the relationships within each lineage, haplotype networks were calculated using NeighborNet and TCS algorithms. Moreover, data were combined with fossil information to construct time‐calibrated trees for the Macaronesian Campanulaceae species. The phylogenetic analyses are largely congruent with current taxon circumscriptions, and all the endemic genera formed monophyletic clades, namely Azorina in Azores; Musschia in Madeira; and Campanula in Cape Verde. The Azorina clade and the Cape Verde endemic Campanula may share a common ancestor in North Africa, and the divergence was dated ca. 12.3 million years ago (Mya). The divergence of the Musschia clade began in the Pliocene ca. 3.4 Mya. Moreover, several examples of intraspecific variation were revealed among the native species with a clear geographic structured patterns, suggesting that cryptic diversity might exist within the native Macaronesian Campanulaceae when compared to the close mainland taxa (e.g., Campanula erinus, Trachelium caeruleum), but additional studies are needed to support the molecular data. This study highlights the power of combining data (e.g., phylogeny and divergence times, with species distribution data) for testing diversification hypotheses within the unique Macaronesian flora, providing useful information for future conservation efforts.
“…Hawaii itself is the only island that is volcanically active, all others being disconnected from the hotspot and inactive for at least 0.75 Myr. This contrasts with the complex geological setting of the Azores, with a western group of two islands located on the North American plate, and a central and eastern group (of five and two islands, respectively) located at the junction between the Eurasian and Nubian lithospheric plate (Ramalho et al, ), and no linear age progression from one side of the archipelago to the other (Ávila et al, ). In addition, some islands in our dataset are younger than the last nine glacial–interglacial cycles (~800 ka) we used to calculate the most frequent and median sea levels.…”
Aim
To quantify the influence of past archipelago configuration on present‐day insular biodiversity patterns, and to compare the role of long‐lasting archipelago configurations over the Pleistocene to configurations of short duration such as at the Last Glacial Maximum (LGM) and the present‐day.
Location
53 volcanic oceanic islands from 12 archipelagos worldwide—Azores, Canary Islands, Cook Islands, Galápagos, Gulf of Guinea, Hawaii, Madeira, Mascarenes, Pitcairn, Revillagigedo, Samoan Islands and Tristan da Cunha.
Time period
The last 800 kyr, representing the nine most recent glacial–interglacial cycles.
Major taxa studied
Land snails and angiosperms.
Methods
Species richness data for land snails and angiosperms were compiled from existing literature and species checklists. We reconstructed archipelago configurations at the following sea levels: the present‐day high interglacial sea level, the intermediate sea levels that are representative of the Pleistocene and the low sea levels of the LGM. We fitted two alternative linear mixed models for each archipelago configuration using the number of single‐island endemic, multiple‐island endemic and (non‐endemic) native species as a response. Model performance was assessed based on the goodness‐of‐fit of the full model, the variance explained by archipelago configuration and model parsimony.
Results
Single‐island endemic richness in both taxonomic groups was best explained by intermediate palaeo‐configuration (positively by area change, and negatively by palaeo‐connectedness), whereas non‐endemic native species richness was poorly explained by palaeo‐configuration. Single‐island endemic richness was better explained by intermediate archipelago configurations than by the archipelago configurations of the LGM or present‐day.
Main conclusions
Archipelago configurations at intermediate sea levels—which are representative of the Pleistocene—have left a stronger imprint on single‐island endemic richness patterns on volcanic oceanic islands than extreme archipelago configurations that persisted for only a few thousand years (such as the LGM). In understanding ecological and evolutionary dynamics of insular biota it is essential to consider longer‐lasting environmental conditions, rather than extreme situations alone.
“…Figure 1A map showing the Azores archipelago within Macaronesia. Within the rectangle on the right details of the Azores islands are shown, with updated islands ages (Sibrant et al 2015; Ávila et al 2016). At the bottom, studied populations of Lactuca watsoniana are shown.…”
Oceanic islands are of particular importance for the conservation of global diversity. Rare island plants with small population sizes and unique genetic patterns resulting from prolonged evolutionary isolation are usually extremely fragile. Therefore, research dedicated to conservation of these plants should consider threat factors, population structure and genetic diversity to enable the development of scientifically supported management programs. For Lactuca watsoniana, Azorean lettuce, we performed a comprehensive population genetic study, unravelling genetic diversity patterns intrinsically related to geographical distances and barriers. Our study showed that genetic diversity levels in island plants can be relatively high even for rare plants.
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