This page features information on a couple of species that I have worked on and my research questions connected to them. These species have both experienced population bottlenecks that resulted in loss of genetic diversity and both are at risk of inbreeding depression.
Inbreeding depression in a recovering ratite: the little spotted kiwi
For my PhD, I focussed on the question of whether or not one of New Zealand's most iconic species is being affected by inbreeding depression. Little spotted kiwi (Apteryx owenii) were downgraded from Vulnerable to Near Threatened by the IUCN in 2008 due to seemingly rapid population growth. However, this species experienced a bottleneck of, at most, five individuals just over 100 years ago and has experienced subsequent bottlenecks due to translocations to form new populations on predator free islands (see below for details). Genetic diversity in this species is known to be low, but the prevalence of inbreeding or inbreeding depression in little spotted kiwi has never been examined.
Little spotted kiwi
The smallest of New Zealand's five species of kiwi, little spots were once widespread throughout New Zealand. Today, only ~1,700 remain. All of these birds exist on predator free offshore islands (and one mainland island sanctuary) and they are all descended from five birds that were translocated to Kapiti Island 100 years ago. While the Kapiti Island population founded by those five birds persisted and grew, little spotted kiwi were extirpated from the mainland by introduced predators and habitat loss by the late 1970s.
Like all kiwi, little spots are flightless and nocturnal and spend the daylight hours sleeping in burrows underground. They are mainly insectivorous. Little spotted kiwi are assumed to be monogamous (although this hasn't been tested genetically) and form long term pair bonds. These birds breed seasonally. The female lays one or two eggs and the male is then responsible for incubation, which can last from 60-80 days. The earliest known age for a reproduction attempt for little spots is two years and estimates for life expectancy in the wild range from 40-80 years.
What did I do?
For my PhD, I studied little spotted kiwi on Long Island and in Zealandia Sanctuary. These populations were chosen because they had the lowest and highest number of founders making them excellent for comparing the effects of different sizes of bottlenecks. My study focused on comparing hatching success and genetic data from these two populations.
Myself and group of dedicated volunteers tracked male kiwi in both sites over a two year period. Males were fitted with radio tags fitted with a special piece of software called Chick Timer, which allowed us to locate males and monitor incubation attempts with minimal disturbance to the birds. We also took feather samples for all the birds we caught so that we could extract DNA and use this to measure genetic diversity and inbreeding in each population.
As part of my research, I asked the following questions:
Sperm health in South Island robins
Following completion of my PhD, I took up a post-doctoral researcher position with the Gemmell lab at the University of Otago. My current research focuses on sperm health in bottlenecked and inbred bird populations. We know that inbreeding frequently effects male fertility, but mechanism underlying this remains unclear. My works aims to untangle the links between inbreeding, sperm DNA fragmentation, sperm motility and morphology and fertility. New Zealand is an excellent place to conduct this research as the majority of bird species here have experienced varying degrees of population bottlenecks due to introduced predators and habitat loss creating a natural experiment with populations that have experienced varying degrees of inbreeding and loss of genetic variation. My work to date in this area has focused on the South Island robin populations at the north of New Zealand's South Island.
South Island robins
New Zealand has two endemic robin species; the North Island robin (Petroica longipes) and the South Island robin (Petroica Australis). In the northern area of the South Island of New Zealand, there are five populations of South Island robin with a well known translocation history (see map below). This has produced an excellent study system to examine the effects of sequential bottlenecks.
Sperm health and semen sampling
The quality of sperm can be measured via a number of metrics, all of which are thought to be linked to fertility. In this study, I'm measuring morphology (length of sperm cells and abnormalities), motility (swimming speed of sperm cells) and DNA fragmentation within the nuclei of the sperm cells. To measure all these characteristics, I have to sample semen from birds in the field.
Semen samples are obtained via a technique called cloacal massage. When male passerine birds are in mating condition, their cloaca swells up. Gently squeezing this swollen area causes semen to be excreted, making it possible to collect small amounts of semen for examination under the microscope.
Sperm motility is measured almost immediately upon collection of a semen sample via a microscope hooked up to a computer loaded with sperm analysis software. This has traditionally proved difficult in the wild because the equipment required is not particularly mobile and has to be kept at around 37 degrees celsius in order to keep the sperm cells alive. I have a mobile laboratory set up that I can take to various field sites, which allows me to conduct motility analyses on-site for as many birds as we can catch.
Semen not used in the motility analyses is stored and returned to the laboratory in Dunedin for morphology and DNA fragmentation analyses. My intention is to combine sperm health data with data on genetic diversity and inbreeding in the robins sampled to establish if the bottleneck history of these populations is impacting their sperm quality and fertility.