Patterns of cranial size variation in two sibling species Plecotus auritus and P. austriacus (Chiroptera: Vespertilionidae) in a contact zone

Abstract

The coexistence in one area of two species with similar ecological requirements can lead to their morphological convergence or divergence. Convergence may be the result of adaptation to new conditions (species share a niche), whereas divergence may be the effect of competition for a resource (species compete for a niche). Compatibility with Bergmann's rule is possible in species with a significant latitudinal range. We tested whether potential differences between two long‐eared bat species are consistent with character displacement or Bergmann's rule by investigating variability in cranial morphology of Plecotus auritus and P. austriacus, which commonly occur in Central and Eastern Europe. We used 111 complete specimens from the allopatric range of P. auritus (nine localities) and sympatric P. auritus and P. austriacus (44 localities) from Poland and Ukraine. A traditional morphometric method was used to evaluate variation in cranial size between the species in their ranges. Discriminant function analysis of cranial dimensions showed larger differences between sympatric populations of P. austriacus and P. auritus than between allopatric P. auritus and a sympatric population of P. austriacus. A subsequent analysis showed that most cranial variables (excluding elements of the skull responsible for prey capture and elements partly associated with echolocation) from the sympatric population of P. auritus are smaller than those homologues from allopatric populations. Larger individuals from the allopatric population originate from the northern part of the study area; however, we did not detect an association of cranial variability with latitude pattern. The variation in size of the cranium between individuals from allopatric and sympatric ranges of P. auritus can be explained by different preferences in each range for prey that vary in hardness. P. auritus consumed significantly more hard‐bodied insects in allopatry than in sympatry. This example is one of few confirmed morphological cases of competitive character displacement.

Close bat species in the Ukrainian fauna: differences and position in the structure of communities

“…Проте має екологічну складову: P. auritus в симпатрії споживає більше дрібних і м'якотілих комах. Цей приклад є одним з небагатьох встановлених на практиці фактів конкурентного зміщення ознак (Postawa et al, 2012).…”

“…Цей процес триває й далі. Відбувається взаємний вплив видів: у аборигенного P. auritus під тиском P. austriacus відбувається конкурентне зміщення ознак (Postawa et al, 2012). Синантропність інвайдера (P. austriacus) у цій парі є мінімальною порівняно з іншими надвидами.…”

Multivariate Analysis of the Skull Size and Shape in Tube-Nosed Bats of the GenusMurina(Chiroptera: Vespertilionidae) from Vietnam

“…Different ecological adaptations especially for food habits are suggested to have produced the species and morphological diversity. Postawa et al (2012) discussed that differentiation in skull morphology of the insectivorous bats is known to correlate with size of prey, hardness of consumed insects, or a combination of these factors; and some congeneric species pairs can utilize similar food habits in allopatry, but they in sympatry, had partitioned the food items and changed skull morphology as character displacements, e.g., between Myotis evotis and M. auriculus (Husar 1976;Gannon and Rácz 2006) and between Plecotus auritus and P. austriacus (Postawa et al 2012). In Vietnam, 11 species of Murina are divided into three different size classes and further differentiated in shape.…”

The patterns and possible causes of global geographical variation in the body size of the greater horseshoe bat (Rhinolophus ferrumequinum)

“…However, analyses of other bat species, such as Pipistrellus kuhlii (Tomassini et al, ), R. ferrumequinum (Budinski et al, ; De Paz, ; Wu et al, ), Plecotus auritus and P . austriacus (Postawa, Zagorodniuk, & Bachanek, ) have failed to support James's rule. In most previous studies of Bergmann's rule in bats, linear measurements (for instance, of the wing and cranium) were used.…”

“…Bergmann's rule/James's rule has been shown in several bat species, including Antrozous pallidus (Kelly, Friedman, & Santana, 2018), Rhinolophus mehelyi (Dietz, Dietz, & Siemers, 2006), Cynopterus sphinx (Storz et al, 2001), Myotis daubentonii (Bogdanowicz, 1990) and Eptesicus fuscus (Burnett, 1983). However, analyses of other bat species, such as Pipistrellus kuhlii (Tomassini et al, 2014), R. ferrumequinum (Budinski et al, 2015;De Paz, 1995;Wu et al, 2014), Plecotus auritus and P. austriacus (Postawa, Zagorodniuk, & Bachanek, 2012) have failed to support James's rule. In most previous studies of Bergmann's rule in bats, linear measurements (for instance, of the wing and cranium) were used.…”