Tuesday, March 19, 2013

[Ornithology • 2013] Hybridisation in the Wild between Great Hornbill Buceros bicornis and Rhinoceros Hornbill Buceros rhinoceros in southern Thailand and its genetic assessment | The impact from habitat fragmentation


Fig. 2. Comparative features among the chicks of the hybrid (I and a–f),
the great hornbill (II and g–l), the rhinoceros hornbill (III and m–r),
and adult males and females of both species
(A–C).
Descriptions of morphological features of the hybrid chick and chicks of the great hornbill and the rhinoceros hornbill were given in Table 1. Please note that the female great hornbill and the male rhinoceros hornbill in II and III are not the real hybrid parents.

Abstract

The great hornbill (Buceros bicornis) and the rhinoceros hornbill (B. rhinoceros) are among the largest Asian hornbill species and they overlap in parts of their ranges. These two species resemble each other in appearance and breeding habits and are sister taxa. In 2004 and 2008, two occurrences of mating in the wild between a male rhinoceros hornbill and a female great hornbill were discovered in the forests of Budo Mountain, southern Thailand. These mated pairs each successfully raised a chick. Morphological and phenotypic characteristics of the chicks most resemble the great hornbill with a few distinctive features hared between both hornbills. Genetic data confirmed these incidences of hybridisation. Analysis of mitochondrial DNA in the hypervariable control region III of these two chicks showed similar patterns to those of their mother, the great hornbill. An investigation of parentage, using 11 microsatellite loci developed from the great hornbill, indicated that the chicks shared at least one allele with the putative mother at all loci. Three different alleles, specifi c for rhinoceros hornbill, were also detected in the chicks. This suggests that the female great hornbill and male rhinoceros hornbill were the true parents of these hybrid chicks, and that the chicks shared the same mother. Our results is the fi rst report of hybridisation between the great hornbill and the rhinoceros hornbill in the wild , and has been genetically confirmed. 

Keywords. — Buceros bicornis, Buceros rhinoceros, hornbill, hybridisation, genetic assessment

Introduction
.............................
In this study, the occurrence of two instances of interspecific mating between pairs of sympatric female great hornbills (Buceros bicornis) and male rhinoceros hornbills (Buceros rhinoceros) were discovered in the forests of Budo Mountain, a part of Budo-Sungai Padi National Park, Thailand. These are sister species in the order Bucerotiformes, resembling each other in appearance, breeding behaviour and genetics (DNADNA hybridisation and phylogenetic study of cytochrome b) (Kemp, 1995; Viseshakul et al., 2011). Both species have a mainly black plumage, a white tail with black band across the center and a large casque (Poonswad, 1993a). There is an area of overlap in the ranges of the species in southern Thailand and Myanmar, the northern Malay Peninsula and Sumatra, but the great hornbill extends north to India and southern China and the rhinoceros hornbill south to Java and Borneo (Kemp, 1995). Females are generally expected to choose their potential mates from superior courtship displays, which are similar in both species with duet calling and headraised postures. In both species, the female hornbill has to trust her mate for his care during imprisoning herself inside the nest tree cavity while laying eggs and brooding the young chicks (Tsuji, 1996). The female generally emerges from the nest before the chick fl edges and then helps her mate feed their chicks until they are virtually independent, when their casques begin to develop (Kemp & Poonswad, 1993). In Thailand, Buceros hornbills have played an important role in the ecological system by acting as large-seed dispersal agents. Great hornbills have been evaluated as Near Threatened, inhabiting several parts of the country, while rhinoceros hornbills are Endangered and inhabit only the southern part (Poonswad, 1993a; Round, 2008).

Fig. 2. Comparative features among the chicks of the hybrid (I and a–f), the great hornbill (II and g–l), the rhinoceros hornbill (III and m–r), and adult males and females of both species (A–C).
Descriptions of morphological features of the hybrid chick and chicks of the great hornbill and the rhinoceros hornbill were given in Table 1. Please note that the female great hornbill and the male rhinoceros hornbill in II and III are not the real hybrid parents.

Although the interbreeding between two sympatric Buceros species has formerly occurred in captive hornbills (Takaki, 1996), this is the first report for hybridisation in wild hornbills. Interestingly, the occurrences took place twice in four years and produced two survived hybrids in the vicinity of Budo Mountain. It is worth noting that the cross-species pairing of hornbills may last for several years and the production of hybrid offspring from these pairings could have unexpected consequences. It is not known if the hybrid birds will have altered behaviour patterns that could affect their ability to survive and subsequently to mate and produce offspring. In addition, the feeding behaviour of the hybrid birds may change, which may have adverse impacts on the ecosystem. Therefore it is of special interest to understand the biological concepts of interbreeding and to follow the survival and evolution of the hybrids. The fertility and continuation of these emerged hybrids would imply that the Great and the rhinoceros hornbills originated from a common ancestor and diverged along with the accumulation of mutations. However, if these hybrids are infertile or suffer reduced viability, and so cannot continue mating, it is most likely that these two hornbills are truely different species.


Siriphatr Chamutpong, Mathurose Ponglikitmongkol, Wutthipong Charoennitkul, Sitthichai Mudsri & Pilai Poonswad. 2013. Hybridisation in the wild between the Great Hornbill (Buceros bicornis) and the Rhinoceros Hornbill (Buceros rhinoceros) in Thailand and its genetic assessment.
The Raffles Bulletin of Zoology. 61(1): 349–358. 
Siriphatr Chamutpong, Wutthipong Charoennitkul, Pilai Poonswad & Mathurose Ponglikitmongkol: A hybrid between Great Hornbill (Buceros bicornis) and Rhinoceros Hornbill (Buceros rhinoceros) in the wild of southern Thailand: The impact from habitat fragmentation. Paper presented at the 5th Intl Hornbill Conference, Singapore, March 2009.


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