Skull shape and Bergmann's rule in mammals: hints from Old World porcupines

Abstract

The genus Hystrix includes eight species of porcupines distributed in Eurasia and Africa, across a broad latitudinal gradient. Our aim was to assess whether porcupine skulls: (1) allow for a reliable interspecific distinction; (2) change in size proportionally with body size; (3) follow the Bergmann's rule. We measured 235 Hystrix skulls from museums and private collections. We tested for differences in skull size and we assessed whether variability in skull shape allows species recognition through a multivariate approach. All Hystrix species considered could be reliably identified by skull shape. Skull size was correlated with body size and species differed in skull shape and size, with skulls of Hystrix javanica and Hystrix africaeaustralis being respectively the smallest and the largest ones. Within Hystrix cristata, the Mediterranean and the sub‐Saharan clades differed for both skull size and shape. Using skull size, we could distinguish among African, mainland Italian and Sicilian populations. Skull size of this species decreased in size for increasing latitude values, contrary to prediction by the Bergmann's rule. Such latitudinal pattern may depend on the adaption of H. cristata to Equatorial African conditions, where the species evolved. In Italy (where H. cristata was introduced in the VI Century AD) and in North Africa, a smaller body size may be due to the local climate, or to a ‘founder effect’.

Out of Europe: Investigating Hystrix cristata (Rodentia: Hystricidae) skull morphometric geographic variability in Africa

“…c. somalensis Lönnberg, 1912, were based on specimens of small size originating from semi-desert regions. Therefore, the available evidence seems to support a role for ecology and local environmental conditions for body size variation in Africa, discarding general theories such as Bergman rule (Mori et al 2019). Cardini et al (2013) found that the largest sized individuals among some Primate species groups are generally found in Central Africa around the Central forest block, with size decreasing towards both West and East.…”

“…Because the influence of size of skull measurement variation is well demonstrated in mammals, we obtained a size-corrected dataset by regressing the condylobasal length versus all other measurements. Indeed, Mori et al (2019) demonstrated that in Hystrix the condylobasal length is a good proxy of skull volume and body size. The obtained size-corrected dataset was used to replicate the above mentioned analyses (PCA and npMANOVA).…”

“…Therefore we are inclined to explain the mismatch between geographic origin of historical museum specimens and the last available distribution map of the species not to recent extirpation events (cfr. Mori et al, 2019) but to a general lack of knowledge especially in the Horn of Africa (cfr. Gippoliti, 2020).…”

Life history and habitat do not mediate temporal changes in body size due to climate warming in rodents

“…Other possible reasons for the widely divergent results concerning temporal changes in body size of rodents could be due to how it is measured. Different studies have used different proxies as a measure of body size i.e., body mass, skull length, cranial size and body length (Alhajeri & Steppan, 2016;Pergams & Lawler, 2009;Villar & Naya, 2018;Yom-Tov & Yom-Tov, 2004)...... Mori et al (2019) showed skull size to be positively correlated with body size across the Hystrix species and confirmed skull size to be a suitable proxy for body size. Similarly, Eastman et al (2012) regarded skull length as a trait positively correlated with body size.…”

Interspecific Aggressions between Crested Porcupines and Roe Deer

“…The crested porcupine, Hystrix cristata, is the largest rodent in Italy [19], living in a number of habitat types, from woodlands to rural environments and to suburban areas [20,21]. Genetics [22], paleontology [23], reproductive phenology [24], behavioral ecology [25] and ectoparasitology [26] strongly suggest a North African origin of the Italian population of this species, which may have occurred after the Fall of the Western Roman Empire (but see also [27,28] for skull morphometrics). The crested porcupine may have evolved in the Pleistocene African savannah, where the ungulate guild was very rich in species [29][30][31].…”