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Dryad

Forelimb morphology as an adaptation for burrowing in kangaroo rat species (genus Dipodomys) that inhabit different soil substrates

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Oct 19, 2023 version files 621.96 KB

Abstract

Among burrowing rodents, forelimb morphology frequently shares an intricate relationship with soil substrates. Soils can vary widely in texture and density, leading to differences in friability, which often requires forelimb specializations in digging animals. Kangaroo rat species (genus Dipodomys) dig and occupy underground burrows, a trait which is essential to their survival. Some members of this genus are restricted to particular types of soil substrates that presumably require species-specific forelimb traits. Here we explored the forelimb morphology and soil substrates inhabited by four Dipodomys species, including two range-restricted species (D. compactus and D. elator) and two widely-ranging species (D. merriami and D. ordii) in an effort to explore the variation in soil usage, forelimb skeletal specializations, and the relationship between these traits. We assessed the size and shape traits of preserved specimen forelimb bones using traditional and geometric morphometric techniques and we extracted soil data associated with the collecting locality of each specimen. We expected the four species to differ in their substrate affinities and forelimb morphology. Specifically, we expected species that inhabit dense soil substrates (e.g., clay-rich soils) to display specialized forelimb morphology typified by an elongated scapula and robust humerus, radius, and ulna bones. The four Dipodomys species differed substantially in their soil associations. We also detected significant morphological differences among Dipodomys species in which forelimb traits allowing for greater mechanical digging ability were found in D. elator, a species that inhabits dense clay-rich soils. These findings suggest that Dipodomys species that inhabit dense substrates may require correspondingly specialized forelimb morphology and that these traits may limit the desirable geographic ranges inhabited by these species. This may provide particularly important information when making conservation decisions on behalf of these species given that, unlike other habitat features, soil substrates cannot be easily modified to suit the needs of the organism.