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the shrew genus Crocidura in Sundaland

Doñana Biological Station describes the evolutionary history

Bornean shrew (Crocidura foetida). The phylogenetic relationships of this endemism have been assessed in this research. The epithet

With 205 extant species, Crocidura represents the most diverse mammalian genus in the world. Although it is widely distributed across Africa and Eurasia, most species are restricted to these continents tropical regions. So what are the processes that have originated this high diversity in the tropics? Researchers of the Doñana Biological Station – CSIC wanted to address this question in their latest study, looking into the drivers that have originated this high diversity of shrews in the tropics, specifically in Sundaland, South-East Asia. The work has been carried out in collaboration with scientists from Geneva, Harvard and Smithsonian museums and Sabah Parks (Malaysia).

This research has specially focused on the island of Borneo. "For unknown reasons, shrews are found at much lower densities on this island than in neighbouring Sumatra, Java or Sulawesi islands" explains Arlo Hinckley, first author of the study and researcher at Doñana Biological Station. "This has historically hampered their study, leaving many questions open, such as how many species are there in Borneo, how and when they originated and how they are distributed."

To answer these questions, researchers conducted several expeditions with a great sampling effort to different mountains in Borneo. Field samples were analysed at a genetic and morphological level, and complemented with additional data obtained from historical specimens hosted at the National Museum of Natural Science (Madrid), Lee Kong Chian Museum (Singapur), Museum of Comparative Zoology of Harvard, Thailand's National History Museum and Museum für Naturkunde (Berlin).

"Evaluating the diversity of this genus through a genetic approach is of great interest given that these shrews are characterized by containing groups of species that are evolutionarily distinct but do not show morphological variation, which frequently makes them go unnoticed", concludes Jennifer Leonard, researcher at Doñana Biological Station. The study also reveals the opposite pattern: shrews living on Mount Kinabalu above 1600m are almost genetically identical to lowland populations of the same mountain, but have a divergent external morphology. "They have cold adaptations: they are bigger and their fur is longer. This might represent an early stage of the speciation process", explains Miguel Camacho, another author and researcher at the EBD-CSIC.

The course of climatic changes during the last four hundred thousand years produced dramatic oscillations in the sea level, connecting and disconnecting the islands of Borneo, Sumatra and Java, among others, with each other and with the continent. It had been traditionally theorized that these periods of intermittent connection created sea barriers that acted as a speciation "pump", boosting biodiversity in this region. However, this research reveals that all the species studied originated earlier, when islands and the mainland were connected. This suggests ecological barriers, such as a possible "savannah corridor", grasslands or swamps, unsuitable for the survival of these shrews could have been important drivers of biodiversity. Such barriers would have driven the isolation between ancestral populations, promoting their differentiation, and the generation of new species over millions of years of evolution.

The research has also confirmed the existence of highly differentiated genetic lineages in the Malay Peninsula, Sumatra, Borneo and Sulawesi. These lineages possibly represent new species but their formal description will require additional expeditions to expand the comparative material (specimens). "This and other studies that we are carrying out on other Bornean small mammals suggest the existence of a remarkable species diversity underestimation present in this region. Cataloguing this biodiversity will require new expeditions and funding", points out Arlo Hinckley. "In biodiversity research, the current funding system favours "office" researchers, which publish a lot using data produced by others, over those who invest a large amount of time in generating this data (and knowledge) which is foundational to the progress of this field, but are thereby less productive, such as taxonomists and field ecologists,".

Taxonomy allows the correct identification of specimens (essential to any biological study), and facilitates the development and implementation of conservation measures. "Studying these animals is difficult. In the field, it was frustrating to sometimes capture only a single individual after several days of work and hundreds of traps, but the result was worth it", adds Miguel Camacho. According to the researcher, it is the most complete study on Bornean shrews so far. Borneo is recognized worldwide as a paradigm of biodiversity but, most of it is little known. "It is worrying to see how behind the green satellite images of Borneo, palm plantations and deforestation predominate on the ground. We are not aware of the great biodiversity lost in the last decades. We hope that our study contributes to protecting the ecological value of this region", concludes the researcher.

Arlo Hinckley points out that this study also highlights the importance of natural history museums in the 21st century: "Thanks to the specimens hosted in museums since the beginning of the 20th century and the advances in genetics, we have been able to obtain information on the evolutionary history of Crocidura and to better understand the biogeography of this region".

Reference: Arlo Hinckley, Miguel Camacho-Sanchez, Manuel Ruedi, Melissa T R Hawkins, Madeleine Mullon, Anna Cornellas, Fred Tuh Yit Yuh, Jennifer A Leonard, Evolutionary history of Sundaland shrews (Eulipotyphla: Soricidae: Crocidura) with a focus on Borneo, Zoological Journal of the Linnean Society, 2021, zlab045, https://doi.org/10.1093/zoolinnean/zlab045


https://academic.oup.com/zoolinnean/advance-article/doi/10.1093/zoolinnean/zlab045/6327494#282934707