Graham A. McCulloch

ONSET OF GLACIATION DROVE SIMULTANEOUS VICARIANT ISOLATION OF ALPINE INSECTS IN NEW ZEALAND

The origin of the New Zealand “beech gap,” a low‐diversity zone in the central South Island corresponding with a disjunction in the distribution of many taxa, has been the focus of biogeographical debate for many decades. Here, we use comparative phylogeographic analysis (COI; H3) of six alpine stonefly genera (116 individuals, 102 localities) to test a vicariant evolutionary hypothesis for the origin of this “biotic gap.” We find strikingly similar phylogeographic patterns in all six genera, with the deepest genetic divergences always found between samples north and south of the beech gap. The magnitude of north‐south genetic differentiation for COI is similar across all six genera (ranging from 0.074 to 0.091), with a test for simultaneous vicariance confirming that divergence is consistent with a single evolutionary event. The concordant cladogenesis detected across multiple taxa is consistent with vicariant isolation caused by the onset of glaciation in the late Pliocene. This study thus indicates an important cladogenetic role for glaciation, an abiotic evolutionary process that is more typically associated with loss of biodiversity.

Do insects lose flight before they lose their wings? Population genetic structure in subalpine stoneflies.

Wing reduction and flightlessness are common features of alpine and subalpine insects, and are typically interpreted as evolutionary adaptations to increase fecundity and promote local recruitment. Here, we assess the impact of wing reduction on dispersal in stoneflies (Plecoptera: Gripopterygidae: Zelandoperla) in southern New Zealand. Specifically, we present comparative phylogeographic analyses (COI; H3) of strong‐flying Zelandoperla decorata (144 individuals, 63 localities) vs. the co‐distributed but weak‐flying Zelandoperla fenestrata species group (186 individuals, 81 localities). The latter group exhibits a variety of morphotypes, ranging from fully winged to completely wingless. Consistent with its capacity for strong flight‐mediated dispersal, Z. decorata exhibited no substantial phylogeographic differentiation across its broad South Island range. Conversely the weak‐flying fenestrata species group exhibited substantial genetic structure across both fine and broad geographic scales. Intriguingly, the variable degrees of wing development observed within the fenestrata species group had no apparent impact on levels of phylogeographic structure, which were high regardless of morphotype, suggesting that even fully winged specimens of this group do not fly. This finding implies that Zelandoperla flight loss occurs independently of wing loss, and might reflect underlying flight muscle reduction.

A time-calibrated phylogeny of southern hemisphere stoneflies: Testing for Gondwanan origins ☆

For more than two centuries biogeographers have attempted to explain why terrestrial or freshwater lineages have geographic distributions broken by oceans, with these disjunct distributions either attributed to vicariance associated with Gondwanan fragmentation or trans-oceanic dispersal. Stoneflies (order: Plecoptera) are a widespread order of freshwater insects whose poor dispersal ability and intolerance for salt water make them ideal candidates for Gondwanan relicts - taxa whose distribution can be explained by vicariant isolation driven by the breakup of Gondwana. Here we reconstruct the phylogenetic relationships among southern hemisphere stoneflies (5 families; 86 genera) using 2864bp of mitochondrial (COI) and nuclear (18S, H3) DNA, with a calibrated relaxed molecular clock used to estimate the chronology of diversification. Our analysis suggests that largely antitropical stonefly sub-orders, Arctoperlaria (northern hemisphere) and Antarctoperlaria (southern hemisphere), were formed approximately 121Ma (95% prior probability distribution 107-143Ma), which may reflect the vicariant rifting of the supercontinent Pangaea. Subsequently, we infer that a single Arctoperlaria lineage has dispersed into southern hemisphere 76Ma (95% range 65-98Ma). The majority of divergences between South American and Australian stonefly lineages appear to coincide with the opening of Drake Passage around 40Ma, suggesting vicariant isolation of these landmasses may be responsible for these biogeographic disjunctions. In contrast, divergences between New Zealand lineages and their sister taxa appear to post-date vicariant timeframes, implying more recent dispersal events.

Does wing reduction influence the relationship between altitude and insect body size? A case study using New Zealand's diverse stonefly fauna

Abstract Researchers have long been intrigued by evolutionary processes that explain biological diversity. Numerous studies have reported strong associations between animal body size and altitude, but insect analyses have often yielded equivocal results. Here, we analyze a collection database of New Zealands diverse endemic stonefly fauna (106 species across 21 genera) to test for relationships between altitude and plecopteran body size. This insect assemblage includes a variety of wing‐reduced (26 spp) and fully winged (80 spp) taxa and covers a broad range of altitudes (0–2,000 m). We detected significant relationships between altitude and body size for wing‐reduced, but not fully winged, stonefly taxa. These results suggest that, while the maintenance of flight apparatus might place a constraint on body size in some fully winged species, the loss of flight may free insects from this evolutionary constraint. We suggest that rapid switches in insect dispersal ability may facilitate rapid evolutionary shifts across a number of biological attributes and may explain the inconsistent results from previous macroecological analyses of insect assemblages.

Polyandry, genetic diversity and fecundity of emigrating beetles: understanding new foci of infestation and selection

The frequency of polyandry and its ecological (and therefore selective) advantages remain unclear, especially in the field, where such tests are seldom conducted. We quantified the fecundity and level of polyandry in field populations of two stored grain beetles, Tribolium castaneum (Herbst) and Rhyzopertha dominica (F.), by comparing resident with dispersing individuals at common sites. Almost all females caught in flight had mated, with paternity analysis from 110 parent–offspring arrays revealing that most females had mated with more than one male (T. castaneum: 90.6, R. dominica: 70.2%). No difference in the extent of polyandry between beetles collected from grain in storage and beetles caught in flight was detected for either species, and the degree of polyandry did not impact overall fecundity. Levels of polyandry were similar to those in recently established (first generation) laboratory cultures of both species. Our results provide the first direct evidence of polyandry in wild populations of T. castaneum and R. dominica, and that females that have mated several times have the potential to produce offspring of multiple genotypes in the field. Females thus invade resource patches (whether previously colonised or not) with considerable genetic diversity to distribute across their offspring, an advantage in a newly colonised site because it increases the chances of her offspring establishing there. This advantageous consequence of polyandry to dispersing individuals, and the fact that most of the individual beetles sampled in the field had mated multiple times, provides justification as to why polyandry should not be viewed as an evolutionary paradox.

Progression of phosphine resistance in susceptible Tribolium castaneum (Herbst) populations under different immigration regimes and selection pressures

Insecticide resistance is an escalating global issue for a wide variety of agriculturally important pests. The genetic basis and biochemical mechanisms of resistance are well characterized in some systems, but little is known about the ecological aspects of insecticide resistance. We therefore designed a laboratory experiment to quantify the progression of phosphine resistance in Tribolium castaneum populations subject to different immigration regimes and selection pressures. Mated resistant females were added to originally susceptible populations under two distinct migration rates, and in addition, half of the populations in each migration treatment were exposed to selection pressures from phosphine fumigation. The progression of phosphine resistance was assessed by screening beetles for the resistance allele at rph2. Phosphine resistance increased slowly in the low migration treatment and in the absence of selection, as expected. But at the higher migration rate, the increase in frequency of the resistance allele was lower than predicted. These outcomes result from the high levels of polyandry known in T. castaneum females in the laboratory, because most of the Generation 1 offspring (86%) were heterozygous for the rph2 allele, probably because resistant immigrant females mated again on arrival. Phosphine resistance was not fixed by fumigation as predicted, perhaps because susceptible gametes and eggs survived fumigation within resistant females. In terms of phosphine resistance progression in populations exposed to selection, the effect of fumigation negated the difference in migration rates. These results demonstrate how species‐specific traits relating to the mating system may shape the progression of insecticide resistance within populations, and they have broad implications for the management of phosphine resistance in T. castaneum in the field. We specify and discuss how these mating system attributes need to be accounted for when developing guidelines for resistance management.

Phylogeography reveals a North Island range extension for New Zealand's only sexually wing-dimorphic stonefly (Stenoperla helsoni)

ABSTRACT Stenoperla helsoni is an endemic New Zealand stonefly characterised by distinctive sexually dimorphic wing loss. Previous distribution records indicated that this species was restricted to the South Islands Southern Alps, although our recent collections of wing-reduced specimens from a site in the Tararua Ranges suggest that this species may extend into the lower North Island. We amplified the mitochondrial COI gene to confirm the identity of North Island specimens, and to assess phylogeographic structuring within the species and genus. North Island specimens were confirmed as S. helsoni, indicating that this species has a much wider geographic range than previously thought. This broad distribution, combined with low levels of intraspecific divergence, suggests that female S. helsoni may be strong fliers, despite males being flightless. Distinct North Island and South Island populations were identified, with a 1.5% divergence between the two populations.

The complete chloroplast genome of the invasive fern Lygodium microphyllum (Cav.) R. Br.

Abstract The Old World climbing fern, Lygodium microphyllum, is a rapidly spreading environmental weed in Florida, United States. We reconstructed the complete chloroplast genome of L. microphyllum from Illumina whole-genome shotgun sequencing, and investigate the phylogenetic placement of this species within the Leptosporangiate ferns. The chloroplast genome is 158,891 bp and contains 87 protein-coding genes, four rRNA genes, and 27 tRNA genes. Thirty-three genes contained internal stop codons, a common feature in Leptosporangiate fern genomes. The L. microphyllum genome has been deposited in GenBank under accession number MG761729.