Gonadal tissue color is not a reliable indicator of sex in rocky intertidal mussels

Abstract

Gonadal tissue coloration was previously thought to be a reliable indicator of sex (male vs. female) in intertidal mussels. However, no investigations have been performed to determine whether color is an accurate representation of sex and to evaluate how this relationship varies throughout the environment. Patterns of gonadal tissue coloration were examined in the mussel Mytilus californianus along 2 environmental axes during the summer of 2004: (1) a food-availability gradient across 4 sites on the central Oregon coast and (2) a vertical (tidal height) stress gradient within each of the sites. Gonadal tissue color was unrelated to food availability. Both male and female mussels at the high edge of the mussel bed had orange gonadal tissue, contrary to conventional wisdom that mussel sex can be determined visually by gonadal color (males = white, females = orange). Field classification based on tissue color is therefore an unreliable indicator of sex in mussels. Environmental stress appears to influence patterns of tissue color (carotenoid pigment concentration) in the intertidal zone.

Evaluating the importance of demographic connectivity in a marine metapopulation

“…Adult mussels were returned to the laboratory, measured with dial calipers, and opened to note the presence or absence of gonad tissue. Sex ratio at all sites was assumed to be 1:1 (Kiyomoto et al 1996) after attempts to determine sex using gonad color were inconclusive (see Petes et al 2008).…”

Misidentification of sex for Lampsilis teres, Yellow Sandshell, and its implications for mussel conservation and wildlife management

“…Thus, the morphometric approach presented in this paper could serve as an example for how to do this for other sexually dimorphic mussel species. During reproductive seasons, sex can be determined by inspecting the gills to determine if an individual is gravid [ 20 – 23 , 59 – 61 ] ( Fig 3c ). This method is frequently used and more correct than determinations based solely on external morphology.…”

“…However, misidentification of sex is also a possible reason for skewed estimates of sex ratios. Methods for assessing sex of mussels vary depending on objectives but can include: 1) using shell shape of sexually dimorphic species [ 17 – 19 ]; 2) visually inspecting gills to assess gravidity [ 20 – 23 ]; 3) extracting gonadal fluid [ 24 – 26 ]; and 4) histological methods [ 14 , 23 , 27 – 30 ]. Of these approaches, shell shape is the easiest method to use to sex mussels because it can be done in the field, does not require vouchering, and costs very little in terms of time and effort.…”

Image analysis method to quantify the effect of different treatments on the visual meat/shell ratio of half‐shelled green lipped mussels (Perna canaliculus)

“…Therefore the mussels were separated by colour (orange = female, pale cream = male). There is a possibility that these colours may not always indicate the correct gender, at least in the case of Mytilus californianus , but this is a convenient method compared with direct microscopic analysis of the gonad tissue and was adopted for the purpose of this study.…”