Systematics of Skuas (Aves: Stercorariidae) with Particular Reference to Evidence from Their Feather Lice (Insecta: Phthiraptera)

Ramli, Rosli (1996) Systematics of Skuas (Aves: Stercorariidae) with Particular Reference to Evidence from Their Feather Lice (Insecta: Phthiraptera). PhD thesis, University of Glasgow.

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Skuas (Aves: Stercorariidae) are large and aggressive seabirds which possess a combination of the features of birds of prey and seabirds. These birds may show two phases (dark and light) of polymorphism in their plumage pattern. They can be found breeding mainly in Arctic and subArctic, or Antarctic and subAntarctic regions. Based on a morphological study, skuas have been separated into two groups; small (genus Sfercorarins) and large (genus Catharacta) skuas. Small skuas are Arctic (S. parasificus). Long-tailed (S. longicaudus) and Pomarine (S. pomarinus) skuas while large skuas are Great (C. skua), Falkland (C. antarctica antarctica), Tristan (C. a. hamiltoni). Brown (T. a. lonnbergi), Chilean (C chilensis), and South Polar (C maccormicki) skuas. However, evidence from other sources (such as behaviour and molecular analyses) suggests a slightly different classification; they can either be clustered together into one group or separated into two groups with a different composition. The fact that a single taxon of large skuas (i.e. Great skua) is geographically separated from others raises issues regarding the evolutionary process. Two possibilities have been suggested: first, some Great skuas migrated to the Southern hemisphere and gave rise to other large skuas. Alternatively, some large skuas from a specific taxon arrived in the Northern hemisphere and gave rise to the Great skua. This study examined both possibilities and tried to determine which hypothesis seemed more likely. Four methods were employed to infer systematic relationships among skuas. These were morphometric analysis, cladistic analysis, a study of the coevolution of skuas and their parasitic lice and examination of mitochondrial DNA. Morphometric and cladistic analyses of seventy two museum specimens and morphometric analyses of eighteen skeletal specimens indicated that skuas should be separated into two groups; small and large skuas. The degree of separation among large skuas was difficult to determine and morphological evidence failed to resolve clear relationship among large skuas. Skuas harbour four genera of feather lice: Haffneria grandis, Austronienopon fuscofascialum, Onadraceps normifer, Saemundssonia stresemamii, S. inexspectata, and S. cephulus. S. iiicxspectata is specific to Long-tailed skua and S. cephahis is specific to Arctic skuas. S. stresemanni is widespread on all skuas, H. grandis only occurs on large skuas and O. normifer and A. fuscofasciatum are scattered on various skua taxa. The lice do not appear to correspond to any specific morphological features on their skua hosts. It was intended to compare mitochondrial DNA (mtDNA) of lice with that of the skua hosts in order to ascertain the coevolutionary relationship between the two but this study failed to extract mtDNA from lice. This failure may be due to sample quality or condition (dried lice instead of fresh or frozen) or quantity of samples. The main conclusions of this study are as follows; first, there are major differences between small and large skuas and skuas should be separated into two groups, small skuas (which consist of Arctic, Long tailed and Pomarine skuas) and large skuas (composed by Great, Tristan, Falkland, South polar, and Brown skuas). Second, there is no indication from morphology and parasitological data that Pomarine skuas arose due to hybridization between members of small and large skuas as suggested by mtDNA data. Third, the evolutionary problems among large skuas are very hard to clarify since evidence relating to this phenomenon is very vague and is difficult to resolve. Therefore, more information from molecular or other approaches is required before this problem can be solved. Finally, while there may be coevolution between skuas and feather lice, there is no evidence for a strict relationship between the two. This may be because skua feather lice possess less host-specific characters or the hosts may have separated from each other too recently to allow time for lice to modify their morphology.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Robert W Furness
Keywords: Systematic biology
Date of Award: 1996
Depositing User: Enlighten Team
Unique ID: glathesis:1996-74920
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 27 Sep 2019 15:11
Last Modified: 27 Sep 2019 15:11

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