10.5061/DRYAD.ZW3R2285B
Wylde, Zachariah
0000-0001-6867-2338
UNSW Sydney
Bonduriansky, Russell
UNSW Sydney
Condition-dependence of phenotypic integration and the evolvability of
genitalic traits in a neriid fly
Dryad
dataset
2020
Australian Research Council
https://ror.org/05mmh0f86
DP170102449
2021-07-09T00:00:00Z
2021-07-09T00:00:00Z
en
https://doi.org/10.1098/rsbl.2020.0124
88997 bytes
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CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
The spectacular diversity of insect male genitalia, and their relative
insensitivity to the environment, have long puzzled evolutionary
biologists and taxonomists. We asked whether the unusual evolvability of
male genitalia could be associated with low morphological integration of
genitalic traits, by comparison with male somatic traits and female
traits. We also asked whether this pattern was robust to variation in
resource availability during development, which affects adult condition.
To address these questions, we manipulated larval diet quality in a
split-brood design and compared levels of integration of male and female
genitalic and somatic traits in the neriid fly, Telostylinus
angusticollis. We found that male genitalic traits were substantially less
integrated than male somatic traits, and less integrated than female
genitalic traits. Female genitalic traits were also less integrated than
female somatic traits, but the difference was less pronounced than in
males. However, integration of male genitalic traits was negatively
condition-dependent, with high-condition males exhibiting lower trait
integration than low-condition males. Finally, genitalic traits exhibited
lower larval diet family interactions than somatic traits. These results
could help explain the unusually high evolvability of male genitalic
traits in insects.
We utilised a full-sib, split-family breeding design where randomly chosen
individuals from these populations were paired to create 17 mating pairs
at 15 ± 2 days old. Each pair was allowed 48 hours to mate within 120 mL
cages provided with a nutrient-rich oviposition medium and access to
sugar, yeast and water ad libitum. Following the 48-hour period, from each
mating pair we transferred 20 eggs to a nutrient-poor larval diet and 20
eggs to a nutrient-rich larval diet, also based on [33]. Upon emergence,
virgin adult offspring were allowed 24 hours for their exoskeletons to
sclerotize fully and then frozen at -80°C for dissection and morphological
measurements. We quantified six genitalic and 12 somatic traits on each of
93 males, and four genitalic and 11 somatic traits on each of 96 females.
All traits were quantified by measuring the lengths of the structures (see
electronic supplementary material), except for testes (TE), for which we
measured area in mm2. For both sexes we used thorax length as an index of
body size [34]. To minimise the loss of samples for multivariate analyses,
missing trait values were replaced with the mean value for the family ×
larval diet × sex combination (where > 3 individuals were available
for that treatment combination). All analyses were carried out using R
3.5.3 [35]. For each set of traits (genitalic and somatic) and group
combinations (sex and larval diet), we estimated morphological integration
as the relative standard deviation of eigenvalues, SDrel (λ) [36]. The
higher the value of SDrel (λ), the more variance is explained by the first
few principal components of the trait matrix, and therefore the higher the
integration. Integration was estimated from principal components analysis
(PCA) performed separately on the correlation matrix for each sex × larval
diet × trait type combination (Figures S3, S4). Standard errors for
integration values were obtained by a Jackknife (n-1 traits) procedure. As
a measure of environmental effects (i.e., larval diet quality), we
computed marginal effect sizes, which indicate the variance explained by
fixed effects [37]. To estimate the maximum genotype × environment
interaction (G × E), we estimated the family × larval diet interaction. We
computed conditional effect sizes, which reflect the variance explained by
both fixed and random effects [37], and estimated the family x larval diet
interaction by comparing the magnitude of the marginal and conditional
effect sizes (see electronic supplementary material for details). Median
parameter values were compared between treatment groups using
nonparametric Kruskal-Wallis or Wilcoxon tests, with trait as the unit of
replication.
Male and female trait values are transformed using log10. Repeatabilities
were obtained by re-positioning each sample/trait and taking multiple
images of the same sample. There are missing values in datasets because
some samples were either damaged or major outliers (>3 sd) in the
data and removed.