Genetic and morphometric data demonstrate alternative consequences of secondary contact inClitarchusstick insects

Abstract

Aim Comparisons of independent secondary contact events provide insights into allopatric speciation. The geographic distribution of Clitarchus stick insects across northern New Zealand corresponds to islands that existed in the Pliocene. Subsequent joining to the mainland provided multiple opportunities for secondary contact. We address the hypothesis that secondary contact has similar effects on parental species, across two peninsulas, due to the simultaneous removal of allopatric barriers. Location Northland, New Zealand Methods We explore how genetic structure relates to morphological variation and biogeographical history of Clitarchus hookeri and C. tepaki. Mitochondrial DNA sequences were used to reconstruct phylogenetical relationships. Population structure was estimated using 14 microsatellite markers. We analysed genital morphology and genetic structure within a biogeographical context to identify the consequences of independent secondary contact events. Results Geographical patterns of genital shape indicate two independent hybrid swarms occur between C. hookeri and C. tepaki. Haplotype distributions and Bayesian cluster analyses reveal C. tepaki from the Aupouri Peninsula are distinguished from C. hookeri on the basis of both genetic structure and morphology. Clitarchus tepaki on the Karikari Peninsula did not group phylogenetically or through Bayesian clustering with C. tepaki from the Aupouri Peninsula. We observed a hybrid swarm along the Aupouri Peninsula. Main conclusions Clitarchus species were separated on Pliocene islands and then subsequently made independent secondary contact as land connections formed. Clitarchus tepaki on the Aupouri Peninsula maintained genetic integrity; whereas we hypothesize genetic swamping has occurred on Karikari Peninsula. Our data demonstrate different outcomes of independent secondary contact events.

Loss and gain of sexual reproduction in the same stick insect

“…These daughters were heterozygous at five or six loci (depending on their father's genotype) where their parents differed. All six genotyped sons were heterozygous at these same loci, with the exception of locus Ch29‐14 (Myers et al, ), where all males genotyped had only the maternal allele observed in the Isles of Scilly, UK population sample. Examination of our genotyping data for 142 individuals indicates that locus Ch29‐14 is sex‐linked.…”

“…This insect species has two large metacentric X chromosomes in females, and one X chromosome in males (Morgan‐Richards & Trewick, ). We inferred that one locus (Ch29‐14; Myers et al, ) was sex‐linked, as males always had a single allele. We confirmed that males inherited their mother's allele but not their father's by genotyping sons.…”

“…For 111 individuals across 15 population samples, we characterized nuclear DNA variation at 10 independent microsatellite loci (Myers et al, ). Multiplex PCR used thermal cycling conditions of 95°C for 5 min, followed by 28 cycles of 95°C for 30 s, annealing temperature of 60°C for 1 min 30 s, and 72°C for 30 s and one additional cycle of 60°C for 30 min.…”

“…In New Zealand, most northern populations of the common diploid stick insect C. hookeri have an even sex ratio and all reproduction is assumed to be sexual (Langton‐Myers, Holwell, & Buckley, ; Morgan‐Richards, Trewick, & Stringer, ; Myers, Buckley, & Holwell, ; Myers, Holwell, & Buckley, ), but males are absent from many southern locations (Figure ). A widespread parthenogenetic lineage appears to have resulted from range expansion by a single mtDNA lineage (Buckley, Marske, & Attanayake, ; Morgan‐Richards et al, ).…”

“…In New Zealand, most northern populations of the common diploid stick insect C. hookeri have an even sex ratio and all reproduction is assumed to be sexual (Langton- Myers, Holwell, & Buckley, 2019;Morgan-Richards, Trewick, & Stringer, 2010;Myers, Buckley, & Holwell, 2015;Myers, Holwell, & Buckley, 2017), but males are absent from many southern locations ( Figure 1 (Buckley, Marske, & Attanayake, 2010;Morgan-Richards et al, 2010). Throughout the southern and eastern North Island and eastern South Island of New Zealand ( Figure 2), reproduction is inferred to be entirely parthenogenetic (Wu, Twort, Crowhurst, Newcomb, & Buckley, 2017); males have been recorded only sporadically and at very low density (Buckley et al, 2010;Morgan-Richards et al, 2010).…”