# Pleistocene Sea‐Level Fluctuation Shapes Archipelago‐Wide Population Structure in the Critically Endangered Lord Howe Island Cockroach Panesthia lata

## TL;DR

This study shows that Pleistocene sea level changes shaped the genetic structure of a critically endangered cockroach species across Lord Howe Island, revealing isolated populations and suggesting genetic rescue as a conservation strategy.

## Contribution

The study provides the first evidence of Pleistocene sea-level impacts on faunal connectivity in the Lord Howe Island Group and identifies inbreeding in cockroach populations.

## Key findings

- The Ball's Pyramid population of Panesthia lata is highly divergent from others.
- Relict cockroach populations on Lord Howe Island show high kinship and inbreeding.
- Genetic rescue from other islands may help conserve the cockroach populations.

## Abstract

The Lord Howe Island Group (LHIG) is one of Australia's most renowned archipelagos. Although a number of studies have investigated the biogeography and genetic diversity of species on Lord Howe Island (LHI) itself, the evolutionary distinctiveness of populations across LHI's satellite islets remains poorly understood. In this study, we explored the genetic structure and health of the Endangered, endemic cockroach Panesthia lata across four islands of the LHIG, using a panel of nuclear single‐nucleotide polymorphisms and complete mitochondrial genomes. Our analyses reveal that the lineage on the permanently isolated islet Ball's Pyramid is highly divergent from the remaining populations, while those on the episodically connected LHI, Roach Island, and Blackburn Island may have diverged as recently as the end of the last interglacial period. These results offer the first evidence that Pleistocene sea level lowstands allowed for historical faunal connectivity across the LHIG. Further, while
P. lata
was believed to have been locally extirpated by rodents on LHI, we discovered a surviving, relict population, albeit with high pairwise kinship indicative of a strong population bottleneck. We also detect relatively high levels of kinship in the other populations, suggesting potential inbreeding that could necessitate ongoing management. Finally, the combination of shallow genetic structure and low diversity suggests that genetic rescue from another island may be a viable strategy to conserve the LHI population of
P. lata
, as well as other species that have been similarly impacted by rodents.

We demonstrate that populations of the critically endangered Lord howe Island cockroach Panesthia lata were connected by land bridges during the last glacial period. Its 4 isolated populations are now highly inbred, suggesting that conservation translocation may be a viable strategy for conservation.