Extreme sequential polyandry insures against nest failure in a frog

Sequential polyandry may evolve as an insurance mechanism to reduce the risk of choosing a mate that is infertile, closely related, genetically inferior or incompatible, but polyandry also might insure against nest failure in unpredictable environments. Most animals are oviparous, and in species where males provide nest sites whose quality varies substantially and unpredictably, polyandrous females might insure offspring success by distributing their eggs across multiple nests. Here, we test this hypothesis in a wild population of an Australian terrestrial toadlet, a polyandrous species, where males construct nests and remain with broods. We found that females partitioned their eggs across the nests of two to eight males and that more polyandrous females gained a significant increase in mean offspring survivorship. Our results provide evidence for the most extreme case of sequential polyandry yet discovered in a vertebrate and also suggest that insurance against nest failure might favour the evolution of polyandry. We propose that insurance against nest failure might be widespread among oviparous taxa and provide an important explanation for the prevalence of sequential polyandry in nature

What factors contribute to an ownership advantage?

In most taxa, owners win fights when defending a territory against intruders. We calculated effect sizes for four factors that potentially contribute to an ‘owner advantage’. We studied male fiddler crabs Uca mjoebergi, where owners won 92% of natural fights. Owners were not more successful because they were inherently better fighters (r=0.02). There was a small effect (r=0.18) of the owner's knowledge of territory quality (food availability) and a medium effect (r=0.29) of his having established relations with neighbours (duration of active tenure), but neither was statistically significant. There was, however, a significant effect due to the mechanical advantage the owner gained through access to the burrow during fights (r=0.48, p<0.005)

Why do fiddler crabs build chimneys?

Chimneys are mud mounds built by fiddler crabs that encircle the entrance to their burrow. Their function in many species is unknown. In Uca capricornis, crabs of both sexes and all sizes build chimneys, but females do so disproportionately more often. There are no differences in the immediate physical or social environments between crabs with and without a chimney. Chimney owners spend less time feeding and more time underground than non-owners. We show experimentally that burrows with a chimney are less likely to be located by an intruder. It is possible that some crabs construct chimneys around their burrow to conceal the entrance and reduce the risk of losing it to an intruder

What are the consequences of being left-clawed in a predominantly right-clawed fiddler crab?

Male fiddler crabs (genus Uca) have an enlarged major claw that is used during fights. In most species, 50% of males have a major claw on the left and 50% on the right. In Uca vocans vomeris, however, less than 1.4% of males are left-clawed. Fights between opponents with claws on the same or opposite side result in different physical alignment of claws, which affects fighting tactics. Left-clawed males mainly fight opposite-clawed opponents, so we predicted that they would be better fighters due to their relatively greater experience in fighting opposite-clawed opponents. We found, however, that (i) a left-clawed male retains a burrow for a significantly shorter period than a size-matched right-clawed male, (ii) when experimentally displaced from their burrow, there is no difference in the tactics used by left- and right-clawed males to obtain a new burrow; however, right-clawed males are significantly more likely to initiate fights with resident males, and (iii) right-clawed residents engage in significantly more fights than left-clawed residents. It appears that left-clawed males are actually less likely to fight, and when they do fight they are less likely to win, than right-clawed males. The low-level persistence of left-clawed males is therefore unlikely to involve a frequency-dependent advantage associated with fighting experience

Alometria no crescimento de Uca mordax (Smith) (Crustacea, Decapoda, Ocypodidae) na Baía de Guaratuba, Paraná, Brasil Allometric growth in the fiddler crab Uca mordax (Smith) (Crustacea, Decapoda, Ocypodidae) from Guaratuba Bay, Parana, Brazil

Um estudo do crescimento relativo da maior quela do macho e do abdome da fêmea foi realizado numa população do caranguejo chama-maré Uca mordax (Smith, 1870) ocorrente no extremo oeste da Baía de Guaratuba, Paraná, sul do Brasil. O comprimento da maior quela (CMQ) foi medido em 319 machos, e a largura do abdome (LAB) em 356 fêmeas. Adicionalmente, seis chama-marés sexualmente indiferenciados foram analisados. A largura da carapaça (LC) foi escolhida como dimensão de referência para ambos os sexos, a qual variou de 1,94 a 20,0 mm para machos, de 2,50 a 18,85 mm para fêmeas, e de 1,94 a 3,15 para os indivíduos sexualmente indiferenciados. A relação entre o LC e CMQ mostrou um ponto de inflexão em 11,70 mm LC nos machos, e entre LC e LAB, em 8,77 mm LC dentre as fêmeas. Os machos (média LC = 14,24 mm) atingiram tamanhos pouco maiores do que as fêmeas (média LC = 13,97 mm). O crescimento foi alométrico positivo durante toda a ontogênese de ambos os sexos, isto é, antes e depois da muda puberal. As equações das relações entre LC e CMQ nos machos foram: logCMQ = -0,542265 + 1,51.logLC para machos juvenis e logCMQ = -1,446281 + 2,37.logLC para machos adultos. Nas fêmeas, a relação entre LC e LAB foi: logLAB = -0,607282 + 1,22.logLC e logLAB = -0,912074 + 1,60.logLC, respectivamente, para juvenis e adultas. Estas dimensões estão relacionadas com as atividades reprodutivas da espécie. O nível de alometria do CMQ dos machos adultos de U. mordax foi o mais alto dentre as espécies do gênero, cujo crescimento relativo desta dimensão foi estudado. A proporção de machos destros foi estatisticamente a mesma daqueles sinistros (1:1).<br>Relative growth of the male major chela and female abdomen was studied in a population of the fiddler crab Uca mordax (Smith, 1870) from Guaratuba Bay, Parana, Southern Brazil. Major chela length (CMQ) was measured from 319 males, and abdomen width (LAB) from 356 females. Also six small sexually undifferentiated crabs were measured. Carapace width (LC) was the reference dimension for both sexes, which ranged from 1.94 to 20.0 mm for males, from 2.50 to 18.85 mm for females, and from 1.94 to 3.15 mm for sexually undifferentiated crabs. Relationship between LC and CMQ showed a transition point at 11.70 mm LC in males, and between LC and LAB, at 8.77 mm LC in females. Males (mean LC = 14.24 mm) showed a slightly greater size than females (mean LC = 13,97 mm). These dimensions had positive allometrical growth during all life for both sexes: before and after the puberal molting. Regressions between LC and CMQ in males read as: logCMQ = -0,542265 + 1,51.logLC for male juveniles and logCMQ = -1,446281 + 2,37.logLC for male adults. In females, the regressions between LC and LAB were: logLAB = -0,607282 + 1,22.logLC for juveniles and logLAB = -0,912074 + 1,60.logLC for adults. These body dimensions are related to reproductive activities of this species. The level of allometry in CMQ of adult males was the highest among Uca species which relative growth of this dimension is known. The handedness had a proportion of 1:1 between right-handed and left-handed males

Comparative analysis of the relative growth of Uca rapax (Smith) (Crustacea, Ocypodidae) from two mangroves in S\ue3o Paulo, Brazil

A study on the relative growth of two populations of Uca rapax (Smith, 1870) was performed primarily to determine the size at onset sexual maturity. The species was sampled monthly in Itamambuca (23º24'43"S and 45º00'73"W) and Ubatumirim (23º20'17.8"S and 44º53'2.2"W) mangroves. Carapace width (CW) and length (CL), abdomen width (AW), major cheliped propodus length (PL) and height (PH) for each sex, and gonopod length (GL) for males were measured with a calliper (0.01 mm). Allometric analyses were used to estimate size at maturity. The relationships that most precisely indicated the size at onset of sexual maturity were AW vs. CW, for females and PL vs. CW, for males. Males and females are mature, respectively at 15.2 and 12.1 mm CW in samples from Itamambuca and 13.5 and 11.2 mm CW in samples from Ubatumirim mangrove. Positive allometric growth of females abdominal width is likely related to the incubation process, while positively allometry growth of male's cheliped almost certainly relates to reproductive behaviour.<br>O estudo do crescimento relativo foi utilizado para determinar quais dimensões evidenciam melhor a maturidade sexual morfológica de Uca rapax (Smith, 1870). Os caranguejos foram coletados mensalmente nos manguezais de Itamambuca (23º24'43"S e 45º00'73"W) e Ubatumirim (23º20'17,8"S e 44º53'2,2"W), em período de maré baixa. Os caranguejos de ambos os sexos foram mensurados com um paquímetro (0,01 mm) quanto à largura da carapaça (LC), comprimento da carapaça (CC) e largura do abdome (LA). Nos machos mensurou-se ainda o comprimento e altura do própodo do quelípodo maior (CPQ e APQ) e comprimento do gonopódio (CG) e, no caso das fêmeas, comprimento e altura do própodo do quelípodo direito (CPQ e APQ). As análises alométricas foram utilizadas para estimar o tamanho da maturidade sexual morfológica. As relações que melhor evidenciaram o tamanho da maturidade foram LA vs. LC para fêmeas e CPQ vs. LC para machos. Machos e fêmeas estão maduros morfologicamente, respectivamente com 15,2 e 12,1 mm de LC em Itamambuca e 13,5 e 11,2 mm de LC no manguezal do rio Ubatumirim. O crescimento alomético positivo da largura do abdomen de fêmeas está relacionado com o processo de incubação, enquanto a alometria positiva do quelípodo dos machos pode estar relacionada ao comportamento reprodutivo