Morphological Variations in the Skulls of Male and Female Persian Fallow Deer (Dama dama mesopotamica)

Introduction

Persian fallow deer (PFD) with the scientific name Dama dama mesopotamica, as one of the rarest deer species in the world, was previously abundant throughout western Asia. Nowadays, they are inhabiting only a small habitat in Khuzestan, Southern Iran, two rather small protected areas in Mazandaran Province (Northern Iran), and some other small areas in the Near and Middle East. This member of the subfamily Cervinae belonging to the family Cervidae is currently listed as endangered by the International Union for Conservation of Nature (Jantschke, 1990; Rabiei and Saltz, 2011; Berger-Tal et al., 2012; Ekrami et al., 2016; Vigne et al., 2016).

Due to the importance of skull anatomy in diverse fields of science, including clinical and surgical practices, wildlife and evolutionary sciences, and sexual dimorphism. Therefore, many studies have been carried out on distinct animals, such as various species of dogs, equines, felines, porcine, sheep, talpas, and rodents (Kieser and Groeneveld, 1992; Evans and McGreevy, 2006; Carreira and Ferreira, 2016; Pitakarnnop et al., 2017; Kyllar et al., 2016; Choudhary and Singh, 2016; de la Barra et al., 2020; Selçuk et al., 2019; Selçuk et al., 2018). Marzban Abbasabadi et al. (2018) evaluated the morphometric differences of the skull between male and female Zell sheep. They found significant in sexual dimorphism between males and females. Parés‐Casanova (2015) analyzed the skulls of adult White Rasquera goat breed to explore sexual dimorph-ism based on geometric morphometric in this local goat breed. Their results demonstrated that the differences in the skull of the two genders may be attributed to the extensive management styles of the animals as under a low anthropogenic influence they tend to reinforce their natural sexual size dimorphism.

In this regard, some studies have evaluated skull anatomy in various species of the Cervidae family. Markov (2014) analyzed the extent of sexual dimorphism in the skull features of red deer (Cervus elaphus L.) in Bulgaria and reviewed the population morphometric variations in the skull of red deer from mountainous and lowland habitats. In addition, there are many studies on skull anatomy in European roe deer (And and Reig, 1993; Sabalinkiene et al., 2017). However, information about PFD skull anatomy is limited. Therefore, the current study aimed to evaluate morphological differences in the skulls of male and female PFDs.

Materials and Methods

Samples Preparation

In cooperation with the Department of Environment of Mazandaran province, Iran, a total of nine PFD skulls or heads (five adult male and four adult female) were obtained from the museum of the Department of Environment and the dead deer of Dasht-e Naz Wildlife Refuge, Sari, Iran protected area during the past two years. Only the skulls of adult PFDs with completely formed dentition were used (Selçuk et al., 2018). The heads and skulls were examined for any skeletal damages or deformities and then the heads were prepared by boiling method. Next, the mandibles were disarticulated from the temporomandibular joint. The samples were numbered and photographed (Canon EOS 4000D, Tokyo, Japan) from dorsal, lateral, ventral, and caudal views. During photography, the camera and the samples were fixed in place to keep the distance and angles of the shots constant.

Morphological Observations

At the first step, the male and female PFD skulls and mandibles were assessed to find remarkable morphological differences. As the horns or cornual process are different between sexes, the other components of the skull and mandible were searched. Afterwards, the accuracy of the found hallmarks was examined.

Morphometric Geometric Studies

As demonstrated in Figures 1 and 2, ten, six, and nine landmark points were defined on the left lateral photos of mandibles and the dorsal and left lateral photos of skulls, respectively. These points were digitized on two-dimensional (2D) images using the TpsDig2 software version 2.16 (Rohlf, 2010).

The adequacy of tangent shape for statistical analysis was investigated utilizing the TpsSmall (Rohlf, 2003). The non-shape inform-ation was removed from landmark configurations applying General Procrustes Ana-lysis The covariance matrices were generated and the shape differences between the two sexes were analyzed by the discriminant function analysis (DFA) in the MorphoJ version 1.02j (Klingenberg, 2011). The patterns of skull and mandible shape differences were illustrated in the wireframe relative to each other for quantification and visualization purposes.

Morphometric Measurements

For morphometric measurements, 11 parameters in the mandibles and 18 parameters in the skulls selected based on the previous studies (Figures 3 and 4, Tables 1 and 2) were calculated utilizing digital Vernier caliper (Digimatic Caliper, Japan) with an accuracy of 0.01 mm. All measurements and observations were blinded (Pitakarnnop et al., 2017; Onuk et al., 2013). Data were analyzed by the independent samples t-test using the SPSS software version 16 (SPSS Inc., Chicago, USA). The level of significance was considered as P-value

Figure 3. Measured parameters in lateral view (A), medial view (B) and dorsal view (C) of the mandible of Persian fallow deer (Dama Dama Mesopotamica): (A) Condyloid fossa to height of mandible (TMA), Condyloid fossa to base of mandible (MMA), Maximum height of mandible (MH), Total length of mandible (ML), Mental foramen to first premolar (MM), Lateral alveolar root to mental foramen (MI), Length of diastema (DL). (B), Caudal border of mandible to beneath of mandibular foramen (CBM), Mandibular foramen to the caudal border of mandible (CM), Mandibular foramen to base of mandible (MB). (C), The interior angle between the bodies of the mandible (Angle)

Table 1. Description of 11 measurements taken from the mandible (see details in Figure 3).