An experimental approach to altering mating tactics in male horseshoe crabs (Limulus polyphemus)

Alternative reproductive tactics are often correlated with phenotype, density, environment, or social context. Male horseshoe crabs(Limulus polyphemus) have two mating tactics that are associatedwith phenotype. Males in good condition arrive at the nestingbeach and spawn while attached to females, whereas those inpoorer condition come ashore unattached and crowd around thenesting couples as satellites, fertilizing eggs through sperm competition. The correlation between mating tactic and phenotypemay be due to males choosing tactics based on condition, orit may be that males that have not found a female choose tocome ashore as satellites. To distinguish between these twopossibilities, I conducted an experiment on male horseshoe crabsin the field at Seahorse Key on the northern Gulf coast ofFlorida. I prevented males from attaching to females by placingsmall plastic bags over the claws they use to attach. The resultsshowed that males in poor condition came ashore as satellites,whereas males in good condition remained at sea. This meansthat mating tactics are cued by information about the male'scondition and not about whether he found a female. The evolutionof phenotype-correlated mating tactics can be represented bya model in which the fitness of each tactic changes with conditionand fitness curves cross. I hypothesize that male horseshoecrabs in good condition have higher fitness when attached and that males in poorer condition to better when unattached.     

Tuning breadth and sex-specific sensitivity in chemosensory neurons of male and female Uca pugnax

Chemosensory neurons of female fiddler crabs (genus Uca) display greater sensitivity to mixtures of food-related stimuli than do neurons in males. This phenomenon represents an interesting contrast to other sex-specific systems, which tend to be in response to cues associated with mating and parental care. This study examined the responses of chemosensory neurons in males and females to ten individual stimuli to determine if sex-specific responses were restricted to a few key compounds, or if the heightened sensitivity of females was broadly distributed. Neurons in males and females responded well to all stimuli, and although fiddler crabs are primarily herbivorous, highly efficacious physiological stimulants included amino acids and amines as well as carbohydrates most closely associated with plant material. The chemosensory neurons are characterized by broad tuning and relatively high response thresholds, when compared to other crustaceans. Most importantly, the investigations revealed a robust pattern in which female neurons displayed elevated responses to all stimuli. Tuning breadth was not shown to be sex-specific, nor were there detectable differences in over-all response profiles. The most likely explanation for these patterns is that the broad sex-specificity in Uca is produced via fundamental alterations in cellular properties associated with chemosensory transduction. Accepted: 29 June 1999     

马铁菊头蝠幼蝠能够辨别种群间回声定位声波差异

蝙蝠的回声定位声波普遍存在地理变化,然而尚不清楚幼蝠在扩散前能否辨别不同种群间的声波差异。本文采用"双选择声学回放实验",研究马铁菊头蝠(Rhinolophus ferrumequinum)幼蝠(1月龄)对回声定位声波地理变化的辨别能力及行为反应。采用4个行为参数衡量幼蝠对本种群(CC)与外种群(JN)回声定位声波的行为反应:每一回放室飞入的次数、飞行时间、停留次数、探测时间。Mann-Whitney U tests表明,马铁菊头蝠1月龄个体对回放声波的行为反应,除每一回放室停留的次数外,其他3个参数均存在显著差异(P0.05),且在本种群声波回放室(CC)的飞行次数和时间以及探测时间均高于外种群声波回放室(JN)。对4个行为参数进行主成分分析,Mann-Whitney U tests表明,回放本种群声波(CC)与外种群声波(JN)之间,第一主成分得分(PC1)存在显著差异(P0.01)。配对T检验表明,幼蝠对本种群声波反应更加强烈(PC1:t10=5.25,P0.001;PC2:t10=2.34,P0.05)。本研究说明马铁菊头蝠幼蝠能够辨别不同种群间回声定位声波的差异。     

Experimentally derived estimates of growth by juvenile Tachypleus tridentatus and Carcinoscorpius rotundicauda (Xiphosura) from nursery beaches in Hong Kong

Juvenile Tachypleus tridentatus and Carcinoscorpius rotundicauda with prosomal widths of between 17.1 and 91.1 mm were obtained from their nursery beaches in Hong Kong. They were kept in the laboratory and fed a mixture of squid, prawn and fish. Prosomal width and wet weight were measured weekly to obtain growth data. Over half of the individuals molted during a five and a half month captivity period. After every ecdysis, prosomal width and wet weight of T. tridentatus grew by averages of 24.2% and 71.5% over pre-molt measurements, respectively. Similar values were obtained for C. rotundicauda, i.e. 24.0% and 77.3%, respectively. Three T. tridentatus with prosomal widths of between 26.5 and 35.0 mm molted twice between 89 and 149 days, leading to an average growth rate of 0.1 mm·day⁻¹ and 0.04 g·day⁻¹ in terms of prosomal width and wet weight, respectively. A positive growth allometry (b coefficient=2.97) was identified, indicating that weight gain for T. tridentatus, and possibly C. rotundicauda, was faster than prosomal width growth after each ecdysis. The effect of temperature on growth was also determined by comparing the percentages of T. tridentatus which molted at ∼28 °C and ∼18 °C. Fifty percent of individuals molted at the former, but only 10% at the latter. This study indicates that Hong Kong horseshoe crabs take a shorter time to reach sexual maturity, as compared with conspecifics in Japan, because they can molt more frequently at higher sediment/water temperatures (∼28 °C) if food is available.     

Spontaneous alternation in marine crabs: Invasive versus native species

Organisms ranging from paramecia to humans tend to explore places that have been least recently explored, which is referred to as spontaneous alternation. Although organisms rely on different sources of information in alternating between places, the emergent behavioral pattern is likely advantageous during exploration and foraging. Under this rationale, continuous spontaneous alternation performance of the invasive green crab, Carcinus maenas was assessed and compared with the native blue crab, Callinectes sapidus in a plus-maze submerged in seawater. For the first time spontaneous alternation behavior was demonstrated in Crustacea (i.e., C. maenas) and significant interspecific differences in alternation performance were observed between the invasive versus the native species. Carcinus maneas exhibited a pronouncedly higher spontaneous alternation performance than C. sapidus. Carcinus maneas on average alternated at levels higher than chance, which was not the case for C. sapidus. These observations point to an additional behavioral mechanism that might result in the competitive success of green crabs over blue crabs in areas where they co-occur. Most of the subjects exhibited asymptotic alternation performance from the onset; there was no improvement in their performance over the course of the experimental session. This finding implies the innate nature of this behavioral policy.     

Shell recruitment in the Mediterranean hermit crab Clibanarius erythropus

Gastropod shells are vital for the majority of hermit crab species, being essential for their survival, growth, protection, and reproduction. Given their importance, shells are acquired and transferred between crabs through several modalities. We conducted observations and experiments at the Asinara Island (Sardinia, Italy) to investigate the efficacy of the different behavioral tactics adopted by the hermit crab Clibanarius erythropus to acquire shells, such as: (1) locomotion and activity at different tidal phases; (2) attendance at shell-supplying sites (simulated predation sites with five different odors: live and dead gastropods, live and dead crabs, predator); and (3) interactions with conspecifics in aggregations on simulated gastropod predation sites. In each tidal phase, locomotion was slow (0.7 cm min^− 1) and, as a consequence, the probability of encountering empty shells and conspecifics was low. Simulated gastropod predation sites quickly attracted a larger number of hermit crabs than the other sites tested. Aggregations seemed to function as shell exchange markets, as previously suggested for other species: the first attendant took the experimental shell and a chain of shell exchanges among conspecifics followed. Our results show that, in C. erythropus, aggregation is the most efficient tactic for the acquisition of new shells, whereas in other species, such as Pagurus longicarpus, it is associated with exploitation ability due to the intense locomotion. The interspecific plasticity in hermit crabs' behavior is confirmed.     

Morphological characterization and molecular phylogeny of Portunoidea Rafinesque, 1815 (Crustacea Brachyura): Implications for understanding evolution of swimming capacity and revision of the family-level classification

Cheliped construction, in particular the teeth pattern on chelae fingers is considered as most important character suit (along with burrowing/swimming apparatus) for the diagnosis of Portunoidea. Heterochelic and heterodontic chelipeds with the molariform tooth in the larger chela and multi-lobed serial teeth are presumably ancestral and most common pattern for the group. New material (mostly species of Thalamitinae Paulson, 1875, Lupocyclus Adamd and White, 1848 and Portunus Weber, 1795 sensu lato) have been combined with the existing sequences from the GenBank to produce molecular phylogenetic reconstructions based on the histone H3 gene fragment and a multi-gene tree (for smaller set of species) based on partial sequences of H3, D1 region of 28S gene and mitochondrial COI gene. These reconstructions have not provided necessary support to the monophyly of Portunoidea sensu lato but indicated the presence of several monophyletic lineages, i.e. Portunidae sensu stricto, Polybiidae + Thiidae + Carcinidae + Pirimelidae, Benthochascon + Geryonidae (to lesser extent), and Ovalipes. Monophyly of the Portunidae sensu stricto is supported by both the H3 and multigene trees and morphological evidence. Swimming capacity probably evolves as a result of parallel evolution in at least three different lineages of portunoids. A new version of the family level classification of Portunoidea and a key to their families are provided with the following taxa: Geryonidae (Geryoninae + Benthochasconinae subfam. nov.), Ovalipidae fam. nov., Brusiniidae Štev?i?, 1991, Thiidae, Pirimelidae, Carcinidae McLeay, 1838 (Carcininae + Portumninae Ortmann, 1893), Polybiidae Ortmann, 1893, and Portunidae Rafinesque, 1815 sensu stricto. The most radical change in the systematics of Portunidae sensu stricto is the final recognition of the polyphyly of Portunus sensu lato and the need for revalidization and re-diagnozing of several taxa that were synonymized by Stephenson and Campbell (1959) and Stephenson (1972) under Portunus. While some subfamilies of the Portunidae (Podophthalminae Dana, 1851, Thalamitinae, and Lupocyclinae Alcock, 1895) are well supported by molecular phylogenies and the presence of morphological synapomorphies, the others need re-assessment.     

长江口芦苇和互花米草盐沼湿地蟹类洞穴分布特征及主要影响因子

蟹类洞穴是蟹类在潮间带盐沼生存、繁衍的特征性结构,具有重要的生态功能。洞穴分布特征及其影响因子的分析,是深入探讨蟹类及其洞穴的生态系统功能的重要基础。2015年10月,在崇明北滩单一芦苇(Phragmites australis)群落,单一互花米草(Spartina alterniflora)群落和芦苇-互花米草混合群落3种典型生境中,对蟹类洞穴的分布特征及其相关的大型底栖动物、植被、沉积物等的特征参数进行了调研与分析。结果表明,生境类型差异对蟹类洞穴分布特征及相关生境因子具有重要影响。蟹类洞穴的分布密度和开口直径在不同生境间存在显著差异(P0.05),且单一芦苇群落生境内洞穴密度要显著高于单一互花米草群落生境(P0.05),洞穴开口直径在单一互花米草生境要显著高于单一芦苇生境(P0.05);大型底栖动物生物量、密度、植物地下部分生物量在不同生境间差异不显著(P0.05),而植株密度、活植株高度、植物地上部分生物量以及沉积物含水率、p H、氧化还原电位在不同生境间存在显著差异(P0.05)。沉积物中值粒径,总氮含量和总碳含量在不同生境间的差异随深度不同会发生变化。不同生境主要生境因子的差异是导致蟹类洞穴分布特征不同的根本原因;蟹类洞穴分布特征受多个生境因子的综合作用。筛选的生境因子的组合虽然与洞穴分布特征具有显著相关性,但相关系数较小。未来研究中需要拓展生境因子涵盖范围,加强多因子综合作用分析。     

A functional analysis of the shift from gill- to lung-breathing during the evolution of land crabs (Crustacea, Decapoda)

The evolution of air-breathing in land crabs is associated with a progressive shift in the primary site of respiratory gas exchange from the diffusion-limited gills used for water-breathing, via a simple 'cutaneous' lung surface to the perfusion-limited, invaginated lung described in the mountain crab, Pseudothelphusa garmani. The reduced diffusion limitation over the lungs facilitates oxygen transfer from air to the tissues at lower ventilation rates but is associated with accumulation of carbon dioxide. A potential respiratory acidosis is buffered by the respiratory pigment haemocyanin and by elevation of haemolymph bicarbonate levels. These changes parallel those described in vertebrates but air-breathing crustaceans maintain relatively low carbon dioxide levels in the haemolymph, either by retaining an aquatic route for its elimination over the reduced gills or by blowing it off across the lung. Maintenance of low carbon dioxide levels may be associated with a limited capacity to buffer against an acidosis due to low levels of circulating haemocyanin (i.e. crustaceans lack red blood cells). This may ultimately limit their survival in air as an acidosis will reduce oxygen transport due to a marked Bohr effect on haemocyanin. The primary role of an invaginated lung may be to reduce rates of water loss in air.