The blowfly Chrysomya latifrons inhabits fragmented rainforests, but shows no population structure

Abstract

Climate change and deforestation are causing rainforests to become increasingly fragmented, placing them at heightened risk of biodiversity loss. Invertebrates constitute the greatest proportion of this biodiversity, yet we lack basic knowledge of their population structure and ecology. There is a compelling need to develop our understanding of the population dynamics of a wide range of rainforest invertebrates so that we can begin to understand how rainforest fragments are connected, and how they will cope with future habitat fragmentation and climate change. Blowflies are an ideal candidate for such research because they are widespread, abundant, and can be easily collected within rainforests. We genotyped 188 blowflies (Chrysomya latifrons) from 15 isolated rainforests and found high levels of gene flow, a lack of genetic structure between rainforests, and low genetic diversity - suggesting the presence of a single large genetically depauperate population. This highlights that: (1) the blowfly Ch. latifrons inhabits a ~ 1000 km stretch of Australian rainforests, where it plays an important role as a nutrient recycler; (2) strongly dispersing flies can migrate between and connect isolated rainforests, likely carrying pollen, parasites, phoronts, and pathogens along with them; and (3) widely dispersing and abundant insects can nevertheless be genetically depauperate. There is an urgent need to better understand the relationships between habitat fragmentation, genetic diversity, and adaptive potential-especially for poorly dispersing rainforest-restricted insects, as many of these may be particularly fragmented and at highest risk of local extinction.

Keywords: Diptera; Ecology; Genetic structure; Habitat fragmentation; Rainforest.

Fig. 1

A The blowfly Chrysomya latifrons which are endemic to southeast Australia and abundant in rainforests; and B the typical rainforest habitat where they can be found (pictured: Washpool National Park, NSW, Australia). Photographs were taken by NB

Fig. 2

Spatial structure of rainforests (represented by dark green) throughout New South Wales, Australia. Data sourced from the Australian State of the Forests 2018 report (https://www.agriculture.gov.au/abares/forestsaustralia/sofr/sofr-2018). Rainforest habitat was defined as “Forest dominated by broad-leaved tree species, typically in wet or sheltered environments and with a closed canopy. Can include areas with non-rainforest species as emergents (trees emerging above the canopy), but where rainforest species dominate the character of the site”. Spatial fragmentation of rainforests at the local scale (10 km) is also represented for three populations (WA, OU, MA) in the right panels

Fig. 3

A dendrogram based on Nei’s genetic distances for individual Chrysomya latifrons (Diptera: Calliphoridae) from 15 rainforest populations. Populations are coloured according to the provided key in order from north (dark purple) to south (yellow). Population abbreviations are provided in Table 1

Fig. 4

Principal component analysis of the filtered dataset of 2693 SNP loci from 15 populations of Chrysomya latifrons (Diptera: Calliphoridae). Populations are coloured according to the provided key in order from north (dark purple) to the south (yellow). Population abbreviations are provided in Table 1

Fig. 5

The mean admixture proportions of populations of Chrysomya latifrons (Diptera: Calliphoridae) that were sampled in the present study. The admixture proportions plotted on the map represent population averages. The bar plots presented on the right reflect individual admixture proportions, sorted by population, where each bar represents a single individual. Full population names are provided in Table 1. All analyses and plotting can be replicated by following the online tutorial provided by Tom Jenkins (https://github.com/Tom-Jenkins/admixture_pie_chart_map_tutorial)

Fig. 6

Geographic distribution of genetic structure and gene flow in Chrysomya latifrons. Full population names are provided in Table 1. a STRUCTURE plot of genetic assignment (K = 3) for 187 individuals. Populations are sorted from top to bottom geographically (north to south). b A relative migration network. Letters represent sampling sites, arrows mark the direction of gene flow, and numbers represent the level of migrant exchange between locations (i.e., effective number of migrants Nm) (Sundqvist et al. 2016). Results of the same analysis with all 15 geographic populations are presented in Supplementary material 2: Table 1