Australian glow-worms (Diptera: Keroplatidae: Arachnocampa spp.) : disbtribution, diversity, identity and management

Claire Baker (2004). Australian glow-worms (Diptera: Keroplatidae: Arachnocampa spp.) : disbtribution, diversity, identity and management PhD Thesis, School of Integrative Biology, The University of Queensland.

       
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Author Claire Baker
Thesis Title Australian glow-worms (Diptera: Keroplatidae: Arachnocampa spp.) : disbtribution, diversity, identity and management
School, Centre or Institute School of Integrative Biology
Institution The University of Queensland
Publication date 2004
Thesis type PhD Thesis
Supervisor Dr. David Merritt
Dr. David Yeates
Dr. Kirsten Scott
Total pages 186
Collection year 2004
Language eng
Subjects L
779903 Living resources (flora and fauna)
270504 Invertebrate Biology
Formatted abstract

The genus Arachnocampa is restricted exclusively to Australasia. In many regions of Australia, glow-worm (Arachnocampa spp.) tourism contributes significantly to the international tourism economy. However, little is known about the insects around which this industry is based. The primary objectives of this study were to identify Arachnocampa distribution in Australia and identify species based on geographic, reproductive, genetic and morphological characters. By highlighting the importance of correct species identification, effective management guidelines can be implemented for specific species found to be at risk in their natural habitat. 

 

Specific habitat requirements (i.e. areas of high humidity), poor Arachnocampa dispersal abilities and fragmentation of habitat have led to the current geographic isolation of Arachnocampa species. Prior to this study, four species of Arachnocampa had been described, including three species endemic to Australia. However, our understanding of Arachnocampa spp. Australia-wide is limited, as most published records of occurrence include no taxonomic or biological investigations of the noted populations. Potential Arachnocampa spp. sites within Australia, not previously documented in the literature were identified based on habitat types within rainforest and caves. From these data, 49 sites were visited, specimens collected, and geographical distribution data was collated and databased. Eight regional groups were defined based on geographic isolation of their specialised habitat. The results from this study greatly increase the known Arachnocampa spp. distribution range to include the wet tropical rainforest of north Queensland and new sites through southeast Queensland, New South Wales and Victoria. These regional groups are further identified through reproductive isolation experiments (Chapter 3), phylogenetic analysis (Chapter 4), and morphological characters (Chapter 5) for evidence of speciation through allopatry. 

 

Male and female Arachnocampa spp. from the same colony will readily mate in the laboratory, so mating trials between individuals were used to determine potential reproductive isolation between and within regional groups at three levels: (1) intra-colony (i.e. samples from the same colony) (n = 8), (2) intra-regional (i.e. samples from the same geographically distinguished region (defined in Chapter 2), but not within the same colony) (n = 7), and (3) inter-regional (i.e. samples from geographically separated regions) (n = 22). The results support geographically based, regional groups as distinct, reproductively isolated species. All eight intra-colony crosses were successful while only one of the 22 inter-regional pairings resulted in mating. However, the eggs from this inter-regional copulation did not hatch, and subsequent repeats of the cross resulted in no mate recognition. Twenty-one inter-regional crosses resulted in no matings, indicating a high degree of reproductive isolation between allopatric populations. Further intraregional separation was indicated in two of the designated regional groups, namely west Victoria and east Victoria. Introductions of adults from within the same colonies (intra-colony) showed these pairs would readily mate in the laboratory trials, but adults would not mate with individuals from another colony within the same designated regional group (intra-regional), separated geographically by 30, 40 and 70 km respectively. While comprehensive pairings were not possible, the results point to strong allopatric speciation. Chapter 3 discusses allopatry in reference to the biological species concept as an instigator of the exhibited reproductive isolation between Arachnocampa species. 

 

To provide phylogenetic evidence supporting species designations, molecular sequence data from 419 base pairs (bp) of the mitchondrial gene fragment cytochrome oxidase II and 414 bp of the mitochondrial gene fragment 16S rDNA were analysed for 37 Australian populations of Arachnocampa, and two outgroup species, A. luminosa, from New Zealand (north and south island localities) and, Orfelia fultoni, from North America (2 localities). The aligned sequence data were analysed in PAUP using parsimony heuristic search algorithms, bootstrapped with 1000 replicates. Phylogenetic analysis of standard and combined data sets strongly supports geographically based regional groupings (Chapter 2) and is largely consistent with results from the reproductive isolation experiments. Phylogenetically, there was no indication of further differentiation within the west Victoria or east Victoria regional groups, as was indicated through reproductive isolation experiments (Chapter 3). The phylogenetic study indicated further delineation within the north Queensland region. Populations from the refugial cave habitats in Girraween National Park, southeast Queensland and populations from the rainforest in Washpool National Park, northern New South Wales, grouped together within the phylogenies. 

 

Morphological examinations of life stages of the eight designated regional groups were undertaken to ascertain any exhibited phenotypic differentiation between the groups and to identify and describe new species. The existing distinction between the subgenera Arachnocampa and Campara, defined on morphological grounds by Harrison (1966), is supported by this study and additional characters are described that further describe the subgenera. Five new species are described: A. buffaloensis (Victoria); A. tropicus (north Queensland); A. gippslandensis (east Victoria); A. otwayensis (west Victoria) and; A. girraweenensis (southeast Queensland/ northern NSW). Further evidence, derived from mating trials and molecular phylogenies, denote further delineation is present within populations in west Victoria (evidence from reproductive isolation), Tasmania (evidence from genetic variation), north Queensland (evidence from genetic variation) and east Victoria (evidence from reproductive isolation and genetic variation). However, these potential species appear to be morpho-cryptic at this level and are not given species status in this study. Each newly identified species was described based on characters that clearly differentiate them. Variation of some characters within populations indicated that a degree of plasticity occurs within this genus. Morphological variation or phenotypic plasticity was also evident between cave and rainforest populations within the same regions. This plasticity, however, is hypothesised as being driven by environmental factors rather than genetic variation. 

 

Given the strict habitat requirements of Arachnocampa spp. and their poor dispersal skills, the genus is often found in isolated habitat where many factors can impact on a colony's sustainability. I identify three key areas of potential Arachnocampa spp. vulnerability and examine case studies specific to each of these areas. Case Study A investigates the practices of commercial glow-worm tour operators in Australia. Each operator was documented and surveyed to identify their annual tourist numbers and issues relating to biological information including glow-worm threats and sustainable management. The study found that a high proportion of commercial operators incorporate substantial biological information in their tours and address threats to glow-worms, including information on human impacts. The study concluded that commercial glow-worm tourism could potentially lead to increased awareness for visitors and the local communities, therefore leading to increased protection for glow-worms and longevity of associated glow-worm tourism in Australia. 

 

Case Study B identified a new species of parasitoid wasp, found to be infecting Arachnocampa spp. populations in north Queensland. The wasp larva develops and pupates in the inactive larva of the north Queensland populations, resulting in the glow-worm's death. The overall density of Arachnocampa spp. colonies in north Queensland was lower than other Australian colonies and parasitism is hypothesised as a reason for the decreased density. High rates of parasitism (31%) were recorded in larvae collected from north Queensland. Movement of the parasitoid to southern Arachnocampa spp. populations could be catastrophic to the multi-million dollar industry surrounding them. Therefore making tourists and tour operators aware of its potential impacts is of great importance to Arachnocampa spp. survival. 

 

Case Study C focuses on a small, fragmented colony of Arachnocampa spp. found in one sub-alpine cave in Victoria. The population is thought to be unable to survive the harsh climatic changes throughout the year outside the cave, and is thus restricted to its current habitat. Isolated habitat was indicated as an important factor for listing this species as threatened. An action management plan is included for follow up after listing.       

Keyword Arachnocampa -- Australia
Additional Notes Page number 87 is missing in the original thesis.

 
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