DOI: 10.5061/dryad.k98sf7mg5
title: Developmental lines of least resistance predict standing genetic covariation but do not constrain plasticity or rapid evolution

description: Some phenotypic dimensions are more developmentally variable than others.
 Such developmental variability (or bias) is common and uncontroversial.
 However, how and at what timescales these biases constrain or facilitate
 the emergence of standing genetic variation, plastic responses, as well as
 adaptation, remains contentious. To investigate the extent to which
 developmental variability shapes genetic variation, plasticity, and
 evolution, we first quantify developmental variability in the shape of the
 dung beetle foreleg — a functional trait critical for the excavation of
 breeding tunnels. We do so by testing how random developmental
 perturbations, manifesting themselves in fluctuating asymmetry, shape
 standing genetic variation within populations. Next, we investigate
 whether such developmental variability is aligned with thermal plasticity
 and recently evolved latitudinal variation. We find that, while
 developmental variability is a strong predictor of standing genetic
 (co)variance (i.e., the G-matrix), latitudinal population differentiation
 and thermal plasticity were unrelated to developmental variability. This
 suggests that, while developmental variability may shape standing genetic
 variation, it does not seem to constrain the evolution of putatively
 adaptive population differentiation and plastic responses. At least in
 this system, developmental biases do not seem to constrain morphological
 differentiation on ecological timescales.
description: <em>Laboratory rearing and data
 acquisition</em> To investigate how developmental
 variability relates to genetic and environmental variation, we revisited a
 common garden study conducted by Rohner and Moczek 2021. In brief, this
 study sampled <em>Onthophagus taurus </em>beetles from one
 location in the native Mediterranean range (Italy) as well as four
 populations in the invasive range in the United States. Wild-caught
 females were brought into the laboratory, where they were then allowed to
 reproduce in plastic containers (27cm × 8cm × 8cm) filled with soil and
 defrosted cow dung. Reproductively active females excavate tunnels in the
 soil and construct so-called ‘brood balls’ underground. These brood balls
 were extracted from the soil using a sieve after five days. Because larval
 growth and adult morphology strongly depend on the size and quality of the
 brood ball, we removed eggs from their natural brood ball and placed them
 in standardized artificial brood balls (consisting of cow dung placed in
 12-well plates). The brood of each female was then split evenly and kept
 at constant 19°C or 27°C. These temperatures were chosen as they
 approximate average soil temperatures during the breeding season at the
 northern and southern range edges in the exotic range (Florida vs.
 Michigan). After adult emergence, beetles were sacrificed and stored in
 70% ethanol. This common garden rearing generated 679 individuals,
 including 321 females. We focused on females because this is the sex that
 primarily excavates tunnels in this species and correspondingly evolved an
 exaggerated tibia morphology.   To increase the sample
 size for the estimation of developmental variability, we added an
 additional 113 laboratory-reared F1+ females that were originally
 collected in North Carolina (the same location as in the common garden
 experiment). This led to a sample size of n = 434 for <em>O.
 taurus</em>. In addition to this focal species, we also added an
 additional 83 female <em>Digitonthophagus gazella</em>. This
 species is morphologically and ecologically similar but shares its most
 recent common ancestor with the <em>Onthophagus</em> lineage
 about 40 million years ago. This species was added to provide an
 additional point of comparison for the statistical comparison of
 covariance matrices (see below). We removed the left
 and right foretibiae of all <em>O. taurus</em> females and
 photographed them twice using a Pixelink camera (M20C-CYL) mounted on a
 Leica M205 stereoscope. For each photograph, the foretibia was placed on a
 piece of modeling clay and positioned in such a way under the stereoscope
 that all features that were used for landmarking were in focus. Each tibia
 was photographed twice. The tibia was removed from the clay and positioned
 anew between pictures to acquire two independent measurements of the same
 sample. We then placed eight two-dimensional landmarks on the pictures
 using TpsDig2. This led to a final dataset for <em>O.
 taurus</em> of 1,736 measurements of 16 variables (434 individuals
 in total × 2 sides (left/right) × 2 independent measurements). All
 landmark coordinates were then aligned simultaneously using Procrustes
 Analysis in the R package <em>geomorph</em>. Centroid size was
 extracted as a measure of structural size. Note that, while the original
 study, Rohner and Moczek 2021, also focused on tibia shape, the analysis
 here is based on a completely independent set of pictures and a slightly
 modified set of landmarks to enable comparisons across species.
description: # Developmental lines of least resistance predict standing genetic
 covariation but do not constrain plasticity or rapid evolution
 [https://doi.org/10.5061/dryad.k98sf7mg5](https://doi.org/10.5061/dryad.k98sf7mg5) This dataset contains landmark coordinates for tibia shape in two dung beetle species. ## Description of the data and file structure The attached Excel file (data_for_dryad2.xlsx) contains the two-dimensional landmark data for a number of specimens. The left and right forelegs of all individuals were photographed twice, and the location of eight landmarks was digitized using TpsDig2. The X-and Y-components of each landmark are listed in the file. These are 'raw' landmarks in unit pixels. These coordinates have not yet been subjected to Procrustes analysis. Missing data are indicated as 'NA'. Variables are defined on a separate sheet in the Excel file as well as below: | variable | description | | :---------- | :------------------------------------------------------------------------------------------------------------------------------- | | individual | individual identifier | | species | species of dung beetle | | population | population of origin | | latitude | latitude of population of origin | | dam.ID | identifier of the dam (i.e., the mother that produced each respective individual) | | temperature | rearing temperature under common garden conditions (19 or 27 degrees Celsius) | | side | indicates whether measurements were taken on the left or right tibia | | measurement | indicates whether measurements were generated during the first or second measurement | | x1-x8 | x-component of the eight two-dimensional landmarks | | y1-y8 | y-component of the eight two-dimensional landmarks | | px\_per\_mm | number of pixels per millimeter. This is used to account for slight differences in magnification between different measurements  |