Evolution of horn shape and sex dimorphism in subspecies of the dama gazelle (Bovidae: Nanger dama (Pallas 1766))
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Greifstrasse 9/10, D-69123 Heidelberg
Online publication date: 2022-11-03
Publication date: 2022-11-03
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Arnd Schreiber   

Greifstrasse 9/10, D-69123 Heidelberg, Germany
Hystrix It. J. Mamm. 2022;33(2):173–186
The horn shape and its sex dimorphism are compared in museum specimens of all geographical populations of the dama gazelle (Nanger dama). Departing from a putatively ancestral morphology prevailing in the west(-central) Sahel zone, a forked cladogenesis is inferred producing the eastern horn type of the red-necked gazelles (N. d. ruficollis) in Sudan and the morphotype of the mhorr gazelles (N. d. mhorr) in the northwest Sahara. The mhorr-horn type is phylogenetically derived as an autapomorphic novelty evolved by a mechanism driven by female sexual mimicry of the male model. Insufficient museum series from the subspecifically vaguely defined populations in the Sahel belt preclude the recognition of one (or even more?) additional horn morphologies in this intercalating region from Senegal to Niger, but any perhaps possible, further type(s), such as a potential horn morphotype in Damergou, Niger, would be weakly differentiated from the ruficollis-horns. Horn morphology suggests moderate subspecies-specific originalities in the fighting behaviours, differing in the intensity of ramming (N. d. mhorr) versus sparring (N. d. ruficollis). The slightly augmented surface area of the eastern morphotype could facilitate thermoregulation, by horn-mediated export of body heat, in the hyperthermic and hyper-arid desert biotope of N. d. ruficollis. Every morphotype is broadly sex-dimorphic, but this dimorphism is reduced in the mhorr gazelles. Andromimicry of female mhorr gazelles, mimicking the sexual phenotype characters of males, is proposed to explain both the diminished sex dimorphism of the horns in this subspecies, and its conspicuously gaudy display and shiny signal coat colours. While the horn ontogeny in female addra gazelles remains unstudied, female mhorr gazelles continued horn length growth during adulthood until old age, but males apparently did not or less so, further raising the complexity of horn shape evolution.
The hospitality and support by the mammal curators or collection managers of the visited natural history museums, as enumerated in the Methods section, is gratefully acknowledged. Dr. Eulalia Moreno, Profesora de Investigación at the Estación Experimental de Zonas Áridas of the Consejo Superior de Investigaciones Científicas (CSIC) at Almeria (Spain), kindly spared the author a travel to Spain by measuring mhorr gazelle horns stored in the collection of her institute. Shortly before his passing the late Prof. Dr. Colin Groves (Canberra) ceded the author a type-written data protocol with measurements from single west Sahelian dama gazelles bequeathed to him in the legacy of the late ungulate taxonomist Dr. Peter Grubb (London), who had obtained these records during a visit at the Institut Fondamental d'Afrique Noire (IFAN) at Dakar (Senegal). Gerhard R. Damm, president of the Applied Science Division in the International Council for Game and Wildlife Conservation, Rivonia (South Africa), provided an update of the dama gazelle data in Rowland Ward’s register of hunting trophies. Prof. Dr. Frank Nürnberg, Hochschule Mannheim, Schwetzingen (Germany), kindly advised on the statistical analyses. Last not least two anonymous reviewers proposed some welcome suggestions whose adoption improved the manuscript.