Browsing by Author "Techow, N M S Mareile"

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    Hybridization and Back-Crossing in Giant Petrels (Macronectes giganteus and M. halli) at Bird Island, South Georgia, and a Summary of Hybridization in Seabirds
    (Public Library of Science, 2015) Brown, Ruth M; Techow, N M S Mareile; Wood, Andrew G; Phillips, Richard A
    Hybridization in natural populations provides an opportunity to study the evolutionary processes that shape divergence and genetic isolation of species. The emergence of pre-mating barriers is often the precursor to complete reproductive isolation. However, in recently diverged species, pre-mating barriers may be incomplete, leading to hybridization between seemingly distinct taxa. Here we report results of a long-term study at Bird Island, South Georgia, of the extent of hybridization, mate fidelity, timing of breeding and breeding success in mixed and conspecific pairs of the sibling species, Macronectes halli (northern giant petrel) and M . giganteus (southern giant petrel). The proportion of mixed-species pairs varied annually from 0.4-2.4% (mean of 1.5%), and showed no linear trend with time. Mean laying date in mixed-species pairs tended to be later than in northern giant petrel, and always earlier than in southern giant petrel pairs, and their breeding success (15.6%) was lower than that of conspecific pairs. By comparison, mixed-species pairs at both Marion and Macquarie islands always failed before hatching. Histories of birds in mixed-species pairs at Bird Island were variable; some bred previously or subsequently with a conspecific partner, others subsequently with a different allospecific partner, and some mixed-species pairs remained together for multiple seasons. We also report the first verified back-crossing of a hybrid giant petrel with a female northern giant petrel. We discuss the potential causes and evolutionary consequences of hybridization and back-crossing in giant petrels and summarize the incidence of back-crossing in other seabird species.
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    Phylogeny and phylogeography of four southern ocean petrels
    (2007) Techow, N M S Mareile; O'Ryan, Colleen; Ryan, Peter G
    This thesis investigates the phylogeography of four southern ocean petrel species in an attempt to resolve taxonomic uncertainties and phylogeography in these species. A large proportion of petrel and albatross species are listed as threatened under Red List criteria, in many cases as a result of threats at sea. Most albatrosses and petrels breed in discrete island colonies and exhibit strong natal philopatry. They may thus be expected to show population divergence, but published studies show that this is not always the case. Most studies to date have concentrated on northern hemisphere species, with mostly albatrosses studied within the southern oceans. White-chinned (Procel/aria aequinoctialis), Spectacled (P. conspicillata) and giant petrels (Macronectes giganteus and M. hal/I) are southern ocean species of Procellariiformes. All four species are threatened by accidental mortality in long line and other fisheries, as well as by introduced predators at their breeding colonies. In order to adequately conserve these species, species limits need to be resolved. Taxonomic uncertainties are an important issue in conservation because often only recognised species receive protection. In addition, islands of origin for birds killed at sea need to be identified. This thesis examines the species status of the Spectacled Petrel (Procel/aria conspicillata), which has been separated from the White-chinned Petrel (P. aequinoctialis) based on morphology and vocalisations, as well as examining the taxonomic status of the two forms of giant petrel, and their phylogeography. Cytochrome b was used to confirm the species rank of the Spectacled Petrel. The decision to support separate species status was based on the lack of shared haplotypes, six fixed mutational differences between the closest haplotypes of the White-chinned and Spectacled Petrel and a sequence divergence of 1.74%. Within Procel/aria, Whitechinned and Spectacled Petrels are sister species, closely related to the wide-ranging Grey Petrel. Within the White-chinned Petrel, two regional populations were found corresponding to colonies in the New Zealand region and the Indian/Atlantic Ocean.Evidence of population expansions were detected in both species and both regional populations of the White-chinned Petrel. Between these two regional populations, the greatest genetiC diversity was within the New Zealand regional population. This result is consistent with the White-chinned Petrel originating in the New Zealand area.