Functional skeletal morphology and its implications for locomotory behavior among three genera of myosoricine shrews (Mammalia: Eulipotyphla: Soricidae)

Abstract

Myosoricinae is a small clade of shrews (Mammalia, Eulipotyphla, Soricidae) that is currently restricted to the African continent. Individual species have limited distributions that are often associated with higher elevations. Although the majority of species in the subfamily are considered ambulatory in their locomotory behavior, species of the myosoricine genus Surdisorex are known to be semifossorial. To better characterize variation in locomotory behaviors among myosoricines, we calculated 32 morphological indices from skeletal measurements from nine species representing all three genera that comprise the subfamily (i.e., Congosorex, Myosorex, Surdisorex) and compared them to indices calculated for two species with well-documented locomotory behaviors: the ambulatory talpid Uropsilus soricipes and the semifossorial talpid Neurotrichus gibbsii. We summarized the 22 most complete morphological variables by 1) calculating a mean percentile rank for each species and 2) using the first principal component from principal component analysis of the indices. The two methods yielded similar results and indicate grades of adaptations reflecting a range of potential locomotory behaviors from ambulatory to semifossorial that exceeds the range represented by the two talpids. Morphological variation reflecting grades of increased semifossoriality among myosoricine shrews is similar in many respects to that seen for soricines, but some features are unique to the Myosoricinae.

A new species of small-eared shrew in the Cryptotis thomasi species group from Costa Rica (Mammalia: Eulipotyphla: Soricidae)

“…The Cordillera de Tilarán in no place reaches an elevation of 2000 m, hence the potential elevational-and areal-distribution of C. monteverdensis is almost certainly restricted to the The mean percentile ranks serve as a general measure of relative locomotory function, from more ambulatory (low ranks) to more fossorial (high ranks). Species are listed in order by increasing mean percentile rank (see Woodman and Gaffney 2014;Woodman and Stabile 2015) Abbreviations of functional indices: SMI shoulder moment index, HRI humeral robustness index, HTI humeral rotation lever index, TTP teres tubercle position index, HEB humeral epicondylar index Tilarán Cordillera, and it is probably endemic to Monteverde. If so, it is the only mammal species endemic to the reserves.…”

“…All of the indices except SMI loaded heavily (>0.940) on the first factor axis, indicating that factor 1 scores provide a reasonable summary of the indices and, thereby, a measure of relative locomotory habitus function (Woodman and Gaffney 2014;Woodman and Stabile 2015). The ranking from this analysis is presented in Table 5.…”

“…We analyzed functionality of the humerus of the new species to assess degree of ambulatory versus fossorial locomotion using measurements and methods described in Woodman and Gaffney (2014) and Woodman and Stabile (2015). Specifically, we calculated five indices of relative fossoriality from seven measurements taken from the humerus and compared them with mean indices from 17 other species of Cryptotis in Woodman and Gaffney (2014).…”

“…Specifically, we calculated five indices of relative fossoriality from seven measurements taken from the humerus and compared them with mean indices from 17 other species of Cryptotis in Woodman and Gaffney (2014). All five indices are expected to increase with increasing fossoriality (Sargis 2002;Samuels and Van Valkenburgh 2008;Woodman and Gaffney 2014;Woodman and Stabile 2015):…”

“…gracilis (n = 45)-COSTA RICA: CARTAGO: Estación El Sitio (KU 160207); 6.5 km ESE of Ojo de Agua, N. slope of Cerro Sákira, 3260 m (USNM 568678); Cerro Asunción, 11,000-11,100 ft (LSU 12641-12650); Cerro de la Muerte, 3335 m (UMMZ 115403); N side summit, The factor scores serve as a general indication of relative locomotory function, from more ambulatory (more negative scores) to more fossorial (more positive scores). Species are listed in order by increasing factor 1 score (see Woodman and Gaffney 2014;Woodman and Stabile 2015) …”