The enigma of reversed asymmetry in lithodid crabs: absence of evidence for heritability or induction of morphological handedness in Lopholithodes foraminatus

Abstract

Mutations or environmental factors that result in reversal of conspicuous left-right asymmetries provide an opportunity to study developmental mechanisms. They may also provide insight into evolutionary changes in asymmetry states within and between species. King crabs (family Lithodidae) have a larger right claw and females typically exhibit a dextrally offset abdomen. Nevertheless, I observed a high incidence of left handedness in laboratory reared box crabs (Lopholithodes foraminatus) and captured the first known egg-bearing female lithodid to exhibit reversed asymmetry. This provided a unique opportunity to characterize the reversed phenotype and to compare the incidence of reversed asymmetry in the offspring of normal and reversed females. Asymmetry of the chelae became apparent in the first postzoeal stage (glaucothoe) and handedness was maintained through subsequent instars. Females with larger left claws developed reversed abdominal asymmetry by the fourth crab stage. No reversed asymmetry was observed in the mandibles of zoea larvae or juveniles of either handedness. The incidence of reversed asymmetry in glaucothoe reared from one reversed and three normal females was high (between 20% and 30%), and independent of maternity (P=0.67). Removal of the right cheliped of fourth stage zoeae, and the major cheliped of glaucothoe, did not reverse the direction of asymmetry. Elevated larval rearing temperature also did not affect the frequency of reversed individuals. This lack of evidence for either heritability or induction of handedness is enigmatic. Further investigation of reversed asymmetry in lithodid crabs may provide valuable insights into the development and evolution of bilateral asymmetries.

What determines direction of asymmetry: genes, environment or chance?

“…In all reported cases of reversed abdominal asymmetry in females, claw asymmetry was also reversed (figure 5a). Mandibular asymmetry, however, did not differ between normal and reversed Lopholithodes foraminatus: a denticulated lobe of the left mandible always fits into an indentation on the right [102]. Significantly, asymmetry did not reverse following autotomy of the larger claw in either normal or reversed individuals [102], so direction of claw asymmetry is clearly fixed and determined globally.…”

“…The pattern of concordance of multiple asymmetries in crustaceans is decidedly mixed. In female king crabs (Lithodidae), the development of asymmetry of the claw and the abdomen (figure 5a) is tightly coupled-reversal in one is associated with reversal in the other-but independent of a seemingly invariant mandibular asymmetry [102]. King crabs are a charismatic family of sometimes large and bizarre looking crabs that include several important commercial species [104].…”

“…(a) Ventral view of adult female king crab, Paralomis formosa, illustrating the enlarged claw on the right (P1*) and a pronounced deflection of the abdomen to the right (dashed curve), both typical of female lithodid crabs. In reversed individuals, the enlarged claw is always on the left, the side to which the abdomen also bends ( pooled data from seven field-collected adults of five species and 13 laboratoryreared juveniles of two species; data and citations in[102]). (b) Adult male fiddler crab, U. stylifera, illustrating the large P1 signalling claw on the right side (P1*) and the elongate style (S) on the tip of the right eyestalk (enlarged in inset).…”

The origin of king crabs: hermit crab ancestry under the magnifying glass

“…The overall body shape of lithodid crabs is highly altered from its hermit crab ancestor. However, pagurid hermit crab asymmetries, influenced by inhabiting dextral gastropod shells (Palmer, 2004), such as pleon and claw asymmetries (McLaughlin & Lemaitre, 1997, 2000McLaughlin et al, 2004;Duguid, 2010), are still present in lithodids (Tsang et al, 2011). Further traces of their pagurid origin can, for example, be found in the mouthparts (Boas, 1924;Jaszkowiak et al, 2015), setation (Keiler & Richter, 2011), internal organ organization (Anker & Paulay, 2013;Keiler et al, 2015) or vascular system (Keiler, Richter & Wirkner, 2013;Keiler et al, 2015).…”

Biennial reproduction with embryonic diapause in Lopholithodes foraminatus (Anomura: Lithodidae) from British Columbia waters

“…Living female crabs were assigned specimen numbers from 1 to 30 (supporting information, Table S1). The individuals assigned specimen numbers 2, 8, 13, and 9 correspond to females A, B, C, and D, respectively, in table 1 of Duguid & Page (2009) and Duguid (2010).…”