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Inferences on mating and sexual systems of two Pacific Cinetorhynchus shrimps (Decapoda, Rhynchocinetidae) based on sexual dimorphism in body size and cheliped weaponry.

Bauer RT, Okuno J, Thiel M - Zookeys (2014)

Bottom Line: The major (pereopod 1) chelipeds of males are significantly larger and longer than those of females.We interpret this evidence on sexual dimorphism as an indication of a temporary male mate guarding or "neighborhoods of dominance" mating system, in which larger dominant robustus males defend females and have greater mating success than smaller males.Based on the sample examined, we conclude that these two species have a gonochoric sexual system (separate sexes) like most but not all other rhynchocinetid species in which the sexual system has been investigated.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, University of Louisiana, Lafayette, Louisiana 70504-2451, USA.

ABSTRACT
Sexual dimorphism in body size and weaponry was examined in two Cinetorhynchus shrimp species in order to formulate hypotheses on their sexual and mating systems. Collections of Cinetorhynchus sp. A and Cinetorhynchus sp. B were made in March, 2011 on Coconut Island, Hawaii, by hand dipnetting and minnow traps in coral rubble bottom in shallow water. Although there is overlap in male and female size, some males are much larger than females. The major (pereopod 1) chelipeds of males are significantly larger and longer than those of females. In these two Cinetorhynchus species, males and females have third maxillipeds of similar relative size, i.e., those of males are not hypertrophied and probably not used as spear-like weapons as in some other rhynchocinetid (Rhynchocinetes) species. Major chelae of males vary with size, changing from typical female-like chelae tipped with black corneous stout setae to subchelate or prehensile appendages in larger males. Puncture wounds or regenerating major chelipeds were observed in 26.1 % of males examined (N = 38 including both species). We interpret this evidence on sexual dimorphism as an indication of a temporary male mate guarding or "neighborhoods of dominance" mating system, in which larger dominant robustus males defend females and have greater mating success than smaller males. Fecundity of females increased with female size, as in most caridean species (500-800 in Cinetorhynchus sp. A; 300-3800 in Cinetorhynchus sp. B). Based on the sample examined, we conclude that these two species have a gonochoric sexual system (separate sexes) like most but not all other rhynchocinetid species in which the sexual system has been investigated.

No MeSH data available.


Related in: MedlinePlus

Sexual dimorphism in Cinetorhynchus sp. B. A Large male (10.8 mm CL) B Female (8.9 mm CL). Scale bars in A and B represent 10 mm C Distal end of chela 1 of a female (11.2 mm CL) showing blackened corneous setae on chela fingers; scale bar represents 0.5 mm D Illustration of tip of chela 1, Rhynchocinetesalbatrossae (from Chace 1997, no scale given), showing form of blackened corneous setae (similar to those shown in Figure 3C) typical of chelipeds 1 and 2 of rhynchocinetids except in large males (e.g., as in this study). C1 cheliped 1; cs corneous setae; dactyl (movable finger); M3 third maxilliped; p propodus; pf propodal (fixed) finger.
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Figure 3: Sexual dimorphism in Cinetorhynchus sp. B. A Large male (10.8 mm CL) B Female (8.9 mm CL). Scale bars in A and B represent 10 mm C Distal end of chela 1 of a female (11.2 mm CL) showing blackened corneous setae on chela fingers; scale bar represents 0.5 mm D Illustration of tip of chela 1, Rhynchocinetesalbatrossae (from Chace 1997, no scale given), showing form of blackened corneous setae (similar to those shown in Figure 3C) typical of chelipeds 1 and 2 of rhynchocinetids except in large males (e.g., as in this study). C1 cheliped 1; cs corneous setae; dactyl (movable finger); M3 third maxilliped; p propodus; pf propodal (fixed) finger.

Mentions: Although sample size is limited in our collection, it is apparent that in both species some males are markedly larger than most females (Figs 1–2, 3A–B). The size-frequency distributions of both species appear bimodal but only the intermediate and larger size classes were sampled by the collection (Fig. 1). Individuals of Cinetorhynchus sp. B reach a much larger size than those of Cinetorhynchus sp. A (Fig. 1A–B). Sexual dimorphism in cheliped weaponry is pronounced in both species. Males bear elongated, heavy major first chelipeds (pereopod 1) with elongated propodi in the larger males (Figs 2A–C, 3A, 4A–B). Additionally, chelipeds of larger males end in a wrench-like subchela (Figs 2A–C, 3A). Major chelipeds of females by comparison are small (Figs 2D–E, 3B, 4A–B) and terminate in a typical chela with equal fingers (Fig. 3B–D). In Cinetorhynchus sp. A, some of the larger males have proportionately much larger chelipeds than the smaller ones (Fig. 4A), while in Cinetorhynchus sp. B, the growth is more linear although with considerable scatter in the data (Fig. 4B). Female first chelipeds (pereopods 1) are shorter and not markedly robust (Figs 2D–E, 3B, 4A–B). As in all known Rhynchocinetidae (e.g., Holthuis 1993: p. 19, Okuno 1996), the chela fingers of both female pereopods 1-2, as well as male pereopods 2, terminate in several, stout, and black (highly sclerotized) setae (Figs 3C–D, 7A) which are reduced (Fig. 7B–C) or lacking in the major chelipeds of larger males (Fig. 7D–E).


Inferences on mating and sexual systems of two Pacific Cinetorhynchus shrimps (Decapoda, Rhynchocinetidae) based on sexual dimorphism in body size and cheliped weaponry.

Bauer RT, Okuno J, Thiel M - Zookeys (2014)

Sexual dimorphism in Cinetorhynchus sp. B. A Large male (10.8 mm CL) B Female (8.9 mm CL). Scale bars in A and B represent 10 mm C Distal end of chela 1 of a female (11.2 mm CL) showing blackened corneous setae on chela fingers; scale bar represents 0.5 mm D Illustration of tip of chela 1, Rhynchocinetesalbatrossae (from Chace 1997, no scale given), showing form of blackened corneous setae (similar to those shown in Figure 3C) typical of chelipeds 1 and 2 of rhynchocinetids except in large males (e.g., as in this study). C1 cheliped 1; cs corneous setae; dactyl (movable finger); M3 third maxilliped; p propodus; pf propodal (fixed) finger.
© Copyright Policy - creative-commons-attribution
Related In: Results  -  Collection

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Show All Figures
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Figure 3: Sexual dimorphism in Cinetorhynchus sp. B. A Large male (10.8 mm CL) B Female (8.9 mm CL). Scale bars in A and B represent 10 mm C Distal end of chela 1 of a female (11.2 mm CL) showing blackened corneous setae on chela fingers; scale bar represents 0.5 mm D Illustration of tip of chela 1, Rhynchocinetesalbatrossae (from Chace 1997, no scale given), showing form of blackened corneous setae (similar to those shown in Figure 3C) typical of chelipeds 1 and 2 of rhynchocinetids except in large males (e.g., as in this study). C1 cheliped 1; cs corneous setae; dactyl (movable finger); M3 third maxilliped; p propodus; pf propodal (fixed) finger.
Mentions: Although sample size is limited in our collection, it is apparent that in both species some males are markedly larger than most females (Figs 1–2, 3A–B). The size-frequency distributions of both species appear bimodal but only the intermediate and larger size classes were sampled by the collection (Fig. 1). Individuals of Cinetorhynchus sp. B reach a much larger size than those of Cinetorhynchus sp. A (Fig. 1A–B). Sexual dimorphism in cheliped weaponry is pronounced in both species. Males bear elongated, heavy major first chelipeds (pereopod 1) with elongated propodi in the larger males (Figs 2A–C, 3A, 4A–B). Additionally, chelipeds of larger males end in a wrench-like subchela (Figs 2A–C, 3A). Major chelipeds of females by comparison are small (Figs 2D–E, 3B, 4A–B) and terminate in a typical chela with equal fingers (Fig. 3B–D). In Cinetorhynchus sp. A, some of the larger males have proportionately much larger chelipeds than the smaller ones (Fig. 4A), while in Cinetorhynchus sp. B, the growth is more linear although with considerable scatter in the data (Fig. 4B). Female first chelipeds (pereopods 1) are shorter and not markedly robust (Figs 2D–E, 3B, 4A–B). As in all known Rhynchocinetidae (e.g., Holthuis 1993: p. 19, Okuno 1996), the chela fingers of both female pereopods 1-2, as well as male pereopods 2, terminate in several, stout, and black (highly sclerotized) setae (Figs 3C–D, 7A) which are reduced (Fig. 7B–C) or lacking in the major chelipeds of larger males (Fig. 7D–E).

Bottom Line: The major (pereopod 1) chelipeds of males are significantly larger and longer than those of females.We interpret this evidence on sexual dimorphism as an indication of a temporary male mate guarding or "neighborhoods of dominance" mating system, in which larger dominant robustus males defend females and have greater mating success than smaller males.Based on the sample examined, we conclude that these two species have a gonochoric sexual system (separate sexes) like most but not all other rhynchocinetid species in which the sexual system has been investigated.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, University of Louisiana, Lafayette, Louisiana 70504-2451, USA.

ABSTRACT
Sexual dimorphism in body size and weaponry was examined in two Cinetorhynchus shrimp species in order to formulate hypotheses on their sexual and mating systems. Collections of Cinetorhynchus sp. A and Cinetorhynchus sp. B were made in March, 2011 on Coconut Island, Hawaii, by hand dipnetting and minnow traps in coral rubble bottom in shallow water. Although there is overlap in male and female size, some males are much larger than females. The major (pereopod 1) chelipeds of males are significantly larger and longer than those of females. In these two Cinetorhynchus species, males and females have third maxillipeds of similar relative size, i.e., those of males are not hypertrophied and probably not used as spear-like weapons as in some other rhynchocinetid (Rhynchocinetes) species. Major chelae of males vary with size, changing from typical female-like chelae tipped with black corneous stout setae to subchelate or prehensile appendages in larger males. Puncture wounds or regenerating major chelipeds were observed in 26.1 % of males examined (N = 38 including both species). We interpret this evidence on sexual dimorphism as an indication of a temporary male mate guarding or "neighborhoods of dominance" mating system, in which larger dominant robustus males defend females and have greater mating success than smaller males. Fecundity of females increased with female size, as in most caridean species (500-800 in Cinetorhynchus sp. A; 300-3800 in Cinetorhynchus sp. B). Based on the sample examined, we conclude that these two species have a gonochoric sexual system (separate sexes) like most but not all other rhynchocinetid species in which the sexual system has been investigated.

No MeSH data available.


Related in: MedlinePlus