DOI: 10.5061/dryad.0rxwdbs08
title: Inheritance of color morphs in Chorthippus dorsatus

description: The green-brown polymorphism of grasshoppers and bush-crickets represents
 one of the most penetrant polymorphisms in any group of organisms. This
 poses the question of why the polymorphism is shared across species and
 how it is maintained. There is mixed evidence for whether and in which
 species it is environmentally or genetically determined in Orthoptera. We
 report breeding experiments with the steppe grasshopper Chorthippus
 dorsatus, a polymorphic species for the presence and distribution of green
 body parts. Morph ratios did not differ between sexes, and we find no
 evidence that the rearing environment (crowding and habitat complexity)
 affected the polymorphism. However, we find strong evidence for genetic
 determination for the presence/absence of green and its distribution.
 Results are most parsimoniously explained by three autosomal loci
 with two alleles each and simple dominance effects: one locus influencing
 the ability to show green color, with a dominant allele for
 green; a locus with a recessive allele suppressing green on the
 dorsal side; and a locus with a recessive allele suppressing green on the
 lateral side. Our results contribute to the emerging contrast between the
 simple genetic inheritance of green-brown polymorphisms in the subfamily
 Gomphocerinae and environmental determination in
 other subfamilies of grasshoppers. In three out of four species
 of Gomphocerinae studied so far, the results suggest one or a few loci
 with a dominance of alleles allowing the occurrence of green. This
 supports the idea that brown individuals differ from green individuals by
 homozygosity for loss-of-function alleles preventing green pigment
 production or deposition.
description: In order to investigate the inheritance of color polymorphism in
 the steppe grasshopper <em>Chorthippus dorsatus</em>, we
 applied a half-sib-full-sib breeding design to produce offspring from
 known parental morph combinations. Our breeding design was implemented
 with field-caught individuals from Jena, Germany (50.94°N, 11.61°E). A
 total of 511 individuals (226 males, 285 females) were sampled as third or
 fourth instar nymphae, ensuring that all individuals were virgin at the
 time of capture. After their final molt, individuals had their color morph
 scored (<em>MorphF </em>and <em>MorphM</em>) and
 were transferred to mating cages. 51 males (<em>MaleID</em>)
 were mated with five females each (249 females in total,
 <em>FemaleID</em>). Each female was kept in a separate mating
 cage, and males were rotated between "their" five mating cages
 every third day. We aimed to equalize morph ratios, but since morph ratios
 were severely skewed in the field, we mated each male to two brown
 females, two dorsal green females, and either a uniform green female, a
 lateral green female, or another brown female. Egg cases were collected
 every seven days and were transferred to Petri dishes lined with moist
 filter paper, and were kept at room temperature for several weeks. Eggs
 were then transferred to refrigerators and kept until spring at about 4°C.
 Diapause was ended in seven cohorts between March and September 2019, with
 one cohort per month (<em>Cohort</em>). Offspring hatched
 after approximately two weeks at room temperature. All offspring from a
 single egg case were transferred to family cages
 (<em>CageID</em>). We assigned full-sib families from the same
 egg case to one of two treatments (<em>Treatment</em>). Half
 of the families were raised in standard plain white housing cages. The
 other half of the families were raised in a more complex, enriched
 environment, in which the floor was lined with patterned green and brown
 foam rubber, a part of a gray or green egg box for cover and climbing, and
 a piece of pipe cleaner for climbing. Multiple egg cases from the same
 mating pair were assigned in equal numbers to both treatments. Offspring
 were scored for color morphs when all individuals of a family had molted
 into the third nymphal stage. Scoring was done by counting the number of
 individuals of each morph per cage (<em>MorphOff </em>and
 <em>nOffsp</em>). 
description: ReadMe sheet contains a description for all variables. Data sheet
 contains the data.