Dermaptera (earwigs) from the Anisolabididae family may be important for pest control but their taxonomy and status in Australia is poorly studied. Here we used taxonomic information to assess the diversity of southern Australian Anisolabididae and then applied cox1 barcodes as well as additional gene fragments (mitochondrial and nuclear) to corroborate classification and assess the monophyly of the putative genera. Anisolabididae morphospecies fell into two genera, Anisolabis Fieber and Gonolabis Burr, based on paramere morphology. Combinations of paramere and forceps morphology distinguished seven morphospecies, which were further supported by morphometric analyses. The morphospecies were corroborated by barcode data; all showed within-species genetic distance < 4% and between-species genetic distance > 10%. Molecular phylogenies did not support monophyly of putative genera nor clades based on paramere shape, instead pointing to regional clades distinguishable by forceps morphology. This apparent endemism needs to be further tested by sampling of earwig diversity outside of agricultural production regions but points to a unique regional insect fauna potentially important in pest control.

We present a chromosome-scale genome assembly for Dryococelus australis, a critically endangered Australian phasmid. The assembly, constructed with Pacific Biosciences continuous long reads and chromatin conformation capture (Omni-C) data, is 3.42 Gb in length with a scaffold N50 of 262.27 Mb and L50 of 5. Over 99% of the assembly is contained in 17 major scaffolds, which corresponds to the species’ karyotype. The assembly contains 96.3% of insect Benchmarking Unique Single Copy Ortholog genes in single copy. A custom repeat library identified 63.29% of the genome covered by repetitive elements; most were not identifiable based on similarity to sequences in existing databases. A total of 33,793 putative protein-coding genes were annotated. Despite the high contiguity and single-copy Benchmarking Unique Single Copy Ortholog content of the assembly, over 1 Gb of the flow-cytometry-estimated genome size is not represented, likely due to the large and repetitive nature of the genome. We identified the X chromosome with a coverage-based analysis and searched for homologs of genes known to be X-linked across the genus Timema. We found 59% of these genes on the putative X chromosome, indicating strong conservation of X-chromosomal content across 120 million years of phasmid evolution.

Transitions to captivity often produce population bottlenecks. On the one hand, bottlenecks increase inbreeding and decrease effective population size, thus increasing extinction risk. On the other hand, elevated homozygosity associated with inbreeding may purge deleterious mutations. Previous empirical studies of purging in captive breeding programs have focused on phenotypic measurements. We test natural selection's ability to purge deleterious mutations following an extreme population bottleneck by analyzing patterns of genetic diversity in wild and captive-bred individuals of the Lord Howe Island stick insect, Dryococelus australis. Dryococelus australis has been bred in captivity for two decades, having passed through an extreme bottleneck—only two mating pairs with few new additions since then. The magnitude of the bottleneck together with high female fecundity but low offspring recruitment set up nearly ideal conditions for the purging of deleterious mutations. As expected, captive-bred individuals had a greater number of long runs of homozygosity compared with wild individuals, implying strong inbreeding in captivity which would facilitate purging in homozygous regions. Stop-codon mutations were preferentially depleted in captivity compared with other mutations in coding and noncoding regions. The more deleterious a mutation was predicted to be, the more likely it was found outside of runs of homozygosity, implying that inbreeding facilitates the expression and thus removal of deleterious mutations, even after such an extreme bottleneck and under the benign conditions of captivity. These data implicate inbreeding and recessive deleterious mutation load in fitness variation among captive and wild D. australis.

Transitions to captivity often produce population bottlenecks. On one hand, bottlenecks increase inbreeding and decrease effective population size, thus increasing extinction risk. On the other, elevated homozygosity associated with extreme bottlenecks may purge deleterious alleles. Previous studies of purging in captive breeding programs have focused on phenotypic measurements and may be confounded with environmental effects. We test the ability of natural selection to purge deleterious alleles following an extreme population bottleneck by analysing patterns of genetic diversity in wild and captive-bred populations of the Lord Howe Island stick insect ( Dryococelus australis ). Dryococelus australis has been bred in captivity for two decades, having passed through an extreme bottleneck – only two mating pairs with few new additions since then. The magnitude of the bottleneck, together with the fact that each female lays hundreds of eggs most of which are not recruited, set up nearly ideal conditions for the purging of deleterious alleles. As expected, captive-bred individuals had a greater number of long runs-of-homozygosity compared to wild individuals, implying strong inbreeding in captivity which would facilitate purging in the homozygous regions. Stop-codon and frameshift alleles were preferentially depleted in captivity compared to other alleles, in coding and non-coding regions. The more deleterious an allele was predicted to be, the more likely it was found outside of runs-of-homozygosity, implying that inbreeding events facilitate the expression and thus removal of deleterious alleles, even after such an extreme bottleneck and under the benign conditions of captivity. These data show that extreme inbreeding has likely decreased the deleterious mutation load of the stick insects, though loss of genetic diversity may make future adaptation more difficult.

Ageing of adult males could be accelerated by both high mating/reproductive effort and fighting for mates. Testing the relative importance of these factors is challenging, however, because males that win fights also tend to have more mates. We used a 2 × 2 experimental design to test how a prolonged (9 week) period of either winning or losing fights, and either high or low reproductive effort (manipulating by varying access to females) interacts to affect male ageing and future reproduction allocation in the mosquitofish, Gambusia holbrooki. We measured telomere length and several life-history traits, including mating effort and ejaculates (sperm count and velocity). After 9 weeks, there were significant differences between winners and losers in their mating effort but not in their ejaculates. Males with a higher past reproductive effort (i.e., access to females) had significantly lower current mating effort and grew more slowly. Males with a higher past reproductive effort also had slower swimming sperm, but only if they were smaller than average in body size. Surprisingly, neither males with a higher past reproductive effort nor males that repeatedly lost fights had shorter telomeres. Our findings show that past social dynamics affect how males allocate resources to reproduction and somatic maintenance.