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    Evolutionary consequences and fitness correlates of extra-pair mating in the tūī, Prosthemadera novaeseelandiae
    (Massey University, 2015) Wells, Sarah Jane
    Animals of many different taxa exhibit sexual dimorphism in phenotypic traits that have evolved through male-male competition and/or female mate choice. Many bird species also engage in extra-pair mating that can exert significant selection pressures on male secondary sexual characters. Studies examining the evolution of sexual dimorphism in birds have demonstrated that the degree of plumage dimorphism is positively related to rates of extra-pair paternity (EPP) among species. In contrast, it is generally argued that sexual size dimorphism (SSD) is not related to EPP but instead is associated with social polygamy. Thus understanding the adaptive function of extra-pair mating may shed light on the evolution of male sexually selected traits. It is argued that females increase offspring fitness by maximising the benefits they receive from males through extra-pair mating. Females are hypothesised to gain direct benefits such as parental care or territory quality through social mate choice, as well as indirect benefits such as compatible genes or good genes benefits through extra-pair mate choice. However, despite much research, the exact adaptive function of female genetic polyandry is still debated. This thesis investigates the influence of sexual selection on the evolution of reproductive behaviours and male secondary sexual characters. We examine correlates and fitness consequences of female within-pair and extra-pair mate choice in the New Zealand tui, Prosthemadera novaeseelandiae. Tui are unusual for a socially monogamous passerine in that they exhibit extreme SSD. They also possess unique ornamental white throat feather plumes which are larger in males, but of which the functional significance is unknown. We discover that tui possess one of the highest rates of EPP of any socially monogamous bird: EPP occurred in 72% of all broods and 57% of all offspring were extra-pair. Our results show that tui exhibit a level of SSD normally associated with strong polygamy, with males being 50% heavier than females. In addition, male body size and ornament size are strong predictors of paternity success. Thus, contrary to current opinion, these findings demonstrate that EPP can be causal in the evolution of SSD. Furthermore, this study provides needed evidence that selective pressures, acting via EPP, can lead to the evolution of male ornaments. Females paired with large social males gained direct benefits that increased offspring survival. Parental ability was not related to male size suggesting that large males may instead provide higher quality territories. Two traits correlating with male extra-pair mating success also predicted offspring fitness: extra-pair young and the offspring of genetically dissimilar sires possessed faster growth rates, and females mated to highly ornamented males overproduced sons to gain offspring with greater reproductive potential. These findings suggest that females gain indirect benefits from extra-pair mate choice, and support both the Fisher-Zahavi good genes and compatible genes hypotheses as functional benefits of female genetic polyandry. Examination of tui parental provisioning rates revealed that males provided significantly less parental care than females. Male ornament size was inversely related to paternal effort, providing further support that ornamentation indicates indirect rather than direct benefits in tui. In addition, males with lower paternity of their broods provided more care than males gaining full paternity. When considered together with female choice for highly ornamented extra-pair males, these findings suggest the existence of alternative male reproductive strategies in which males trade-off investment in offspring with mating effort in response to their residual reproductive potential. Tui are unusual in that they possess several attributes commonly associated with social polygyny, such as extreme SSD, multiple male traits, and reduced paternal care. Although the selection pressures leading to the evolution of ornamentation and SSD in tui remain to be clearly resolved, the relationship between these two traits is likely complex. We argue that these traits may have evolved through male-male competition but are reinforced by female choice for dominant males. This study substantially furthers our knowledge of tui mating behaviours and makes a significant contribution towards understanding the functional significance of male traits and EPP. Finally, our findings have implications for sexual selection theory pertaining to the evolution of SSD.
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    The anatomy and histomorphology of the uropygial gland in New Zealand endemic species : a thesis presented in partial fulfilment of the requirements for the degree of Master of Zoology at Massey University, Palmerston North, New Zealand
    (Massey University, 2013) Reynolds, Sian
    Considering that there are more than 10,000 species of birds on earth, and that the uropygial gland is the most prominent integument gland in this vertebrate group, it is puzzling that little is known about its morphology and function. The current hypotheses for the function of the uropygial gland can be placed into four groups: 1) feather maintenance; 2) water-proofing; 3) intraspecific communication/health; and 4) defence against predators and/or parasites. Several studies have examined these hypotheses, although no general function for the uropygial gland has been established. This thesis aimed at reducing the gap in knowledge of the uropygial gland by investigating New Zealand birds. The purpose of this study was to examine the anatomical and histological structure of the uropygial gland in New Zealand birds and to investigate the defence hypothesis as a function of the gland specifically in brown kiwi (Apteryx mantelli). Anatomical and histological analyses of the uropygial glands from brown kiwi, great spotted kiwi (Apteryx haastii), hihi (Notiomystis cincta), New Zealand bellbirds (Anthornis melanura), tui (Prosthemadera novaeseelandiae), and saddleback (Philesturnus carunculatus) were carried out. The anatomy and histology of all glands were compared both within family and order and to those available from other species worldwide. The defence hypothesis function of the uropygial gland was investigated using the tick species Ixodes anatis from the skin of brown kiwi. This study revealed a range of uropygial gland characteristics in the kiwi, hihi, New Zealand bellbird, tui, and saddleback that were not know to previously exist in other species. For example kiwi uropygial glands were found to possess eight primary sinuses. Comparison of the New Zealand passerines revealed that bellbirds possess the largest gland in relation to body size out of the four species. The uropygial secretion of brown kiwi may play a role in parasite repellence as both males and female ticks were deterred from the secretion. Based on histomorphology I suggest that rather than a single function, the gland may have species/group functions. However, this hypothesis still remains enigmatic due to the lack of birds studied to date.
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    The vocalisation of tui (Prosthemadera novaeseelandiae) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Conservation Biology, Massey University, Albany, New Zealand
    (Massey University, 2011) Hill, Samuel David
    This study investigates the vocalisation of tui and its individual, gender and regional variations. A population of tui at Tawharanui Regional Park was studied in order to investigate the characteristics, diversity, gender variation and seasonal variations of tui vocalisation. In 2.4 hours of recordings collected from 48.5 hours of field sampling between July and December, 2010, 303 distinctly different songs were recorded, which included four types of vocalisations. These were long-range broadcasting songs, short-range interactive songs, alarm calls and distress calls. In 30 randomly selected songs from different individuals, 264 distinctly different syllables were observed. The level of syllable repetition and syllable sharing between individuals were low. A significantly greater proportion of trill and a significantly lower minimum frequency were found in long-range songs than in short-range songs. A greater proportion of trill in the long-range songs is possibly due to: 1. Long trill components being more effective in long-range transmission than short bouts of trill, 2. High frequency trill is less likely to suffer from sound degradation in open habitats than lower frequency syllables and 3. Trill is costly to produce and may advertise the genetic quality of the singer, therefore are used more in long-range broadcast songs rather than in short-range interactive songs. Significantly lower minimum frequencies in long-range songs is likely to facilitate the transmission of sound further in distance and through vegetations. Minimum frequencies may also correlate with the size of the singer, which is likely important information to advertise in long-range songs for mate attraction and territory defence. Male songs were not significantly longer in duration than female songs. Males however had a much larger repertoire of syllables and male songs contained a significantly larger proportion of rapid multiple note repetition syllables, both of which are likely sexually-selected traits linked to genetic diversity and the ability to defend high-quality territories. Tui songs in breeding season had a greater proportion of trill components compared to that in non-breeding season. Trill has been found to be another sexually-selected characteristic of males. Statistical analysis also suggested that at the population level, tui sing a greater number of songs during the non-breeding season than during the breeding season. However this observation is likely due to stronger territorial behaviour of tui in breeding season resulting in a reduction in the density of birds in one specific area. Tui songs recorded from the Chatham Islands were compared to those from Tawharanui Regional Park in order to explore the regional variation in tui vocalisation. Long-range male songs recorded from Tawharanui had a significantly greater proportion of trill, inflection points in the terminal note and longer song duration than that from Chatham Island. These characteristics have all been demonstrated as being sexually-selected traits that are positively correlated with male genetic diversity, suggesting that the genetic diversity of individuals in the mainland population is higher than that of the island population. The acoustic adaptation hypothesis could also help to explain the significantly higher proportion of trill component in the long-range songs of the mainland population, as the mainland study site contained more open vegetation than the Chatham Islands sites and trill transmits more effectively in such habitats. The mainland population also had a larger song repertoire and syllabic diversity at the population level and the two populations exhibited 7.5% syllable similarity when comparing syllable repertoires. There was, surprisingly, no significant overall difference in the multivariate dispersion of spectral characteristics when comparing both short and long-range songs between populations, however this is likely due to the effect of sample size. Differences in habitat type, opportunities for immigration and emigration, levels of male-male competition and sexual selection pressures all likely drive the overall variation observed when comparing the structure of both long-range and short-range songs and would explain the difference observed in the song and syllable repertoire between the two populations. This study has provided baseline data of song type, individual, gender, seasonal and regional differences in tui vocalisation, which will help develop our understanding of communication in tui. Knowledge of tui vocalisation can help in determining individuals’ reproductive potential, past breeding success and the role of songs in tui breeding success. Such information is important for the conservation of tui, particularly in areas where tui population is declining and requires conservation efforts and management such as translocation.