Population genetics of White-eared Honeyeaters in New South Wales
For my dissertation I have organized and led four months of fieldwork in New South Wales, Australia to sample the White-eared Honeyeater across an aridity gradient. My goal is to assess the population genetic status of the White-eared Honeyeater across New South Wales and interrogate how sex chromosomes may be involved in adaptation to aridity. Most of New South Wales is a highly fragmented landscape due to agricultural land-use change and White-eared Honeyeaters are now primarily only found in protected areas including national parks, state forests, and conservation areas. I am calculating population genetic parameters, delimiting evolutionarily significant units (ESUs), and conducting selection scans to determine which genomic compartments are involved in local adaptation to aridity.
Evolution of neo-sex chromosomes in Australian honeyeaters
For my dissertation, I am studying the evolution of neo-sex chromosomes in Australian songbirds called honeyeaters. I seek to understand i) how neo-sex chromosomes facilitate adaptation across environmental gradients, and ii) the patterns and consequences of recent recombination loss. The Australian honeyeaters provide a perfect system to study this, first because their neo-sex chromosomes are nascent compared to the ancestral sex chromosomes in birds, and second because many honeyeaters are distributed across an extreme environmental gradient from the cooler, wet coast to the arid, hot interior of Australia. I incorporate genomic and transcriptomic data and long read sequencing to study these topics in a comparative genomic framework. I am particularly passionate about connecting natural history knowledge with genomic data.
Burley*, J. T., Orzechowski*, S. C. M., Sin, S. Y. W., & Edwards, S. V. (2022). Whole-genome phylogeography of the blue-faced honeyeater (Entomyzon cyanotis) and discovery and characterization of a neo-Z chromosome. Molecular Ecology. https://doi.org/10.1111/mec.16604
*co-first authors
Ecological impacts of an invasive apex predator
Burmese pythons are negatively impacting multiple trophic levels in the Everglades and their cryptic coloration impedes detection and removal efforts. Dense wading bird breeding aggregations--colonies--represent an potential attractant for pythons, who have drastically reduced other prey bases like small mammals. Colonies and nests on tree islands isolated by water are vulnerable because pythons are semi-aquatic and use arboreal habitat.
For my master's degree, I tested the prediction that Burmese pythons are directly impacting wading bird reproductive success through nest predation. Using trail cameras aimed at nests, I documented predation of both Great Egret and White Ibis nests by multiple pythons. Wading bird reproduction in the Everglades is generally limited by hydrology, not native predators, and therefore wading birds have been used as indicator species for the Comprehensive Everglades Restoration Program. As novel nest predators in wading bird colonies, pythons may be disrupting restoration predictions and consequent practices. My research indicates the need for future monitoring which will inform the potential need for python management action in colonies.
Orzechowski, S. C. M., Romagosa, C. M., & Frederick, P. C. (2019). Invasive Burmese pythons (Python bivittatus) are novel nest predators in wading bird colonies of the Florida Everglades. Biological Invasions, 21(7), 2333–2344.
Fig 1. Nest cams from my second year of monitoring in the central Everglades.
eDNA occupancy modeling to evaluate the threat of an invasive predator
For my master's degree, I used environmental DNA to test the prediction that Burmese pythons are attracted to wading bird colonies of the Florida Everglades. Environmental DNA (eDNA) is a popular conservation tool for detecting rare or cryptic species when traditional survey methods fail. Pythons are remarkably cryptic and detection probability using visual surveys has been estimated to be less than 1%. Wading birds breed colonially in tree islands surrounded by aquatic marsh. I collected eDNA water samples at both colony and control islands during the wading bird breeding season. Then, I ran Bayesian hierarchical occupancy models to compare python eDNA occupancy rates. I found that python occupancy is higher at colonies during the breeding season, which is a cause for concern since I have also found that pythons are novel wading bird nest predators. My results underscore the need for a python management plan in wading bird colonies.
Orzechowski, S. C. M., Frederick, P. C., Dorazio, R. M., & Hunter, M. E. (2019). Environmental DNA sampling reveals high occupancy rates of invasive Burmese pythons at wading bird breeding aggregations in the central Everglades. PloS One, 14(4), e0213943.
Fig 1. Estimated posterior distributions of python site occupancy (ψ) in colony versus control sites.