DOI: 10.5061/dryad.sxksn0317
title: Lack of assortative mating might explain reduced phenotypic differentiation where two grasshopper species meet

description: Hybridization is an evolutionary process with wide-ranging potential
 outcomes, from providing populations with important genetic variation for
 adaptation to being a substantial fitness cost leading to extinction.
 Here, we focussed on putative hybridization between two morphologically
 distinct species of New Zealand grasshopper. We collected Phaulacridium
 marginale and Phaulacridium otagoense specimens from a region where
 mitochondrial introgression had been detected and where their habitat had
 been modified by introduced mammals eating the natural vegetation and by
 the colonization of many non-native plant species. In contrast to
 observations in the 1970s, our sampling of wild pairs of grasshoppers in
 copula provided no evidence of assortative mating with respect to species.
 Geometric morphometrics on the pronotum shape of individuals from areas of
 sympatry detected phenotypically intermediate specimens (putative
 hybrids), and the distribution of phenotypes in most areas of sympatry was
 found to be unimodal. These results suggest that hybridization associated
 with anthropogenic habitat changes has led to these closely related
 species forming a hybrid swarm, with random mating. Without evidence of
 hybrid disadvantage, we suggest a novel hybrid lineage might eventually
 result from the merging of these two species.
description: # Lack of assortative mating might explain reduced phenotypic
 differentiation where two grasshopper species meet Authors: Mary
 Morgan-Richards, Maurine Vilcot, Steven A. Trewick The data are
 mitochondrial DNA sequences and morphometric values relating to variance
 among Phaulacridium (Insect, Orthoptera, Acrididae) grasshoppers that were
 sampled in Aotearoa (New Zealand). The morphometric data are
 'traditional' metrics of eight nonindependent variables
 comprising three size differences (hind femur length, hind tibia length,
 and tegmina length), three ratios and two angles of the pronotum margin in
 dorsal view; and geometric coordinates derived from twelve geometric
 landmarks were identified and digitized around the perimeter of the dorsal
 surface of the pronotum. DNA sequences result from Sanger sequencing of
 PCR products from 95 individual grasshoppers. With previous data, this
 provides an alignment of nucleotide data for 243 individuals. ##
 Description of the data folder: ### Folder: Data This folder contains four
 files including: 1. Phaulacridium COI.phy: Fasta file containing
 Mitochondrial DNA cytochrome oxidase subunit 1 sequence data, 755bp long.
 2. PC_eigenvalues.csv 3. PC_scores.txt 4. Phaulacridium_measurements.csv:
 individual information and morphometrics measurements Variables in
 Phaulacridium_measurements.csv: * Code, Individuals: individual
 identifiers * Lname, LocationName, L: short name, long name and number
 associated to the sampling location * Sex: sex of the individual * In
 copula: whether the individual was caught in pair or alone * Pair_code: if
 caught in pair, the identifier of the pair * Latitude, Longitude: sampling
 coordinates * Year, Date: sampling date * PA1: pronotum angle 1 as the
 lateral carinae pronotum angle with vertical sulcus (°) * PA2: pronotum
 angle 2 as the Lateral carinae pronotum angle with first transverse sulcus
 (°) * PW1: pronotum width (mm) * PW2: pronotum width at the narrowest
 point (mm) * PW3: pronotum width at the widest point (mm) * PL: pronotum
 length (mm) * TeL: tegmina length (mm) * FL: femur length (mm) * FW: femur
 width across the third muscle band (mm) * TL: tibia length(mm) * HL: head
 length (mm) * HW: head width (mm) * HW/HL, FL/FW, PW1/PW2, PW3/PL: ratios
 of the above variables ### Folder: Output This folder contains 4 CSV files
 that are direct outputs from the scripts detailed below. Variables not
 defined above: * cluster_trad: cluster info based on traditional
 morphometrics * uncertainty_trad: uncertain species identification based
 on traditional morphometrics * Species_traditional: species identification
 based on traditional morphometrics * Female: female assignment *
 Uncertainty_Female: uncertain female assignment * Male: male assignment *
 Uncertainty_Male: uncertain male assignment * Pair_type: in copula male
 and female species combination (marginale/marginale, marginale/otagoense,
 otagoense/otagoense) * d'Agostino Omnibus: d’Agostino omnibus
 normality test * DB: Bannockburn Sluicings sample location * DQ: Quartz
 Reef sample location * HR: Hawkesdun Road sample location = DH * AW:
 Awaroa sample location * AG: Graveyard Gully sample location = AxG * AL:
 Little Valley Road sample location = AxL * AM: Asample location * TE:
 Tekapo east sample location = TeE * TW: Tekapo west sample location = TeW
 * Code: unique sample code for each specimen * V1-V4: assignment
 probabilities to each of the 4 clusters from Gaussian mixture model
 assignment based on pronotum geometric landmark data (V1 *P. marginale*
 female, V2 *P. otagoense* male, V3 *P. otagoense* female, V4 *P.
 marginale* male) * Species_geometric: species identification based on
 geometric data * cluster_pronotumPC2: assignment from second principal
 component of pronotum shape variation * Sex_geometric: sex identification
 based on geometric data * marginale_membership: assignment score to
 marginale taxon group * otagoense_membership: assignment score to
 otagoense taxon group ## Sharing/Access information: The data are also
 available publicly at the research group website (link in Related Works
 section). Part of the data and their derivation were previously reported
 in the following *Insect Conserv Divers* article, which includes details
 of PCR and sequencing of DNA, and 'traditional' morphometric
 data collection: Sivyer, L., Morgan-Richards, M., Koot, E. and Trewick,
 S.A. (2018), Anthropogenic cause of range shifts and gene flow between two
 grasshopper species revealed by environmental modelling, geometric
 morphometrics and population genetics. *Insect Conserv Divers*, 11:
 415-434. ## Code/software: Procrustes analysis, PCA, and ANOVA from
 pronotum landmarks were made on MORPHOJ. All other analysis were performed
 in R, and are reproducible with this folder. Detailed annotations and the
 library used are provided throughout the scripts. *
 01_Traditional_morphometrics.R: This R script reproduces the clustering
 and species identification from the measurement data *
 02_Geometric_morphometrics.R: This R script reproduces the clustering
 analysis, normality test and from pronotum landmarks