New Insights into the Male Morphotypes of the Amphidromous Shrimp Macrobrachium olfersii (Weigmann, 1836) (Caridea: Palaemonidae) and a Discussion on Social Dominance Hierarchies.

Male morphotypes in a population may lead to the development of social dominance hierarchies in crustacean species. Currently, Macrobrachium is the decapod crustacean genus with the largest record of species that present the development of hierarchies. Macrobrachium olfersii has morphological characteristics that indicate the presence of male social dominance within its populations. Thus, the present study tested the hypothesis of the occurrence of male morphotypes in M. olfersii through morphometric and morphological analysis of the chelipeds. Sampling was carried out from March 2018 to October 2021 in seven points along the Jequitinhonha River, Northeast Brazil. A total of 264 males were collected with carapace length (CL) ranging from 4.01 to 23.70 mm. Morphological sexual maturity size was estimated at 8.95 mm CL. The morphometric and morphological analysis confirmed the presence of three adult male morphotypes: M1, M2, and M3. The characterization of the different morphotypes was mainly due to the variation in size, shape, and morphology of the largest cheliped of the second pair of pereopods. Most morphometric relationships differed significantly (p < 0.01) among the three morphotypes, mainly between M3 against M1 and M2. The variation in the propodus shape was also evident. This trait and the angulation of the spines differed significantly between morphotypes (p < 0.01), with the propodus of morphotype M3 being more robust and carrying a greater number of spines than the others. The occurrence of social dominance and the exaggerated development of a cheliped (weapon) can be advantageous for dominant individuals when they need to compete for resources. This morphological trait can provide these individuals with advantages during fights and guarantee access to the best resources, whether they are shelter, food, or sexual partners. Our results add new information to the biology of M. olfersii, as well as the genus Macrobrachium, and the occurrence of social dominance in species of this group. In addition, by describing these morphotypes in detail, using a set of complementary morphological and morphometric techniques, it is possible to access the differential morphology along the M. olfersii males, as well as confirm a life history trait found in several Macrobrachium species.

Larval development of the crab Amphithrax hemphilli (Rathbun, 1892) (Decapoda, Brachyura, Mithracidae) described from laboratory-reared material.

The complete larval development of Amphithrax hemphilli was described, illustrated, and compared with that of the previously described larvae of the genus Mithrax sensu lato. Specimens of A. hemphilli were sampled from the northeastern Brazilian coast. The larval development of A. hemphilli consisted of two zoeal stages and one megalopa. Amphithrax hemphilli shows morphological features in all stages of larval development that differ from those observed in other species of Amphithrax, Mithrax, and Maguimithrax. In the first larval stage, A. hemphilli was the only species with two aesthetascs on the antennule and the coxal endite of the maxillule with five setae. In the second larval stage, A. hemphilli was distinguished from the other species of the genus Mithrax sensu lato by the presence of five setae on the basial endite of the maxilla and 26 setae in the scaphognathite of the maxilla. Finally, the megalopa stage of A. hemphilli is characterized by the number of aesthetascs on the three-segmented exopod of the antennule, the setation of both the endopod of the third maxilliped, and pleonites 1-6. Based on the results obtained in the present study, we verified that the more advanced the larval stage, the more distinct characteristics are observed among species of the genus Mithrax sensu lato, facilitating the identification of species through later larval stages.

Sexual system, reproductive cycle and embryonic development of the red-striped shrimp Lysmata vittata, an invader in the western Atlantic Ocean.

Several decapod crustaceans are invaders, but little is known about the biological characteristics that potentiate the success of these decapods in invaded ecosystems. Here, we evaluate and describe some aspects of the reproductive biology and development of Lysmata vittata, an invasive shrimp species in the Atlantic Ocean. In addition, we intend to provide important insights into the biology of invasion by comparing the reproductive traits of this shrimp with some of the predictions about aquatic invasive species. We used experimental and laboratory observations to evaluate the functionality of protandric simultaneous hermaphroditism (PSH), the macro and microscopic development of the ovarian portion of the ovotestes, the reproductive cycle, and the embryonic development of L. vittata. We confirm the functionality of PSH in L. vittata. This shrimp has a rapid reproductive cycle; the ovarian portion of the ovotestes develops (mean ± SD) 6.28 ± 1.61 days after spawning. Embryonic development also occurs over a short time, with a mean (± SD) of 8.37 ± 0.85 days. The larvae hatch without macroscopically visible yolk reserves. Our study provides evidence that the invasive shrimp L. vittata has reproductive and embryonic developmental characteristics (i.e., short generation time and high reproductive capacity) that may be favorable to the establishment of populations during invasive processes.

Morphological and molecular analyses confirm the occurrence of two sympatric Lysmata shrimp (Crustacea, Decapoda) in the southwestern Atlantic.

An integrative approach was used, combining morphological and molecular analyses, to provide the first report of Lysmata lipkei and L. vittata in Sergipe State, Brazil, and confirm that both species are invasive of the Atlantic Ocean. Lysmata shrimps were sampled in the estuary region of the Vaza-Barris river, Sergipe State, northeastern Brazil, and identified as L. lipkei (n = 8) and L. vittata (n = 20). To molecular phylogenetic analysis was used 16S DNA fragments, comparing 26 species of the Lysmata-Exhippolysmata clade and two species of the genus Merguia (outgroup). Phylogenetic analysis indicated the absence of consistent genetic divergence (p distance < 0.018) between specimens from Atlantic and Indo-Pacific oceans. We conclude that L. lipkei and L. vittata have successfully invaded the western Atlantic and are also present in Sergipe State, northeastern Brazil.

Morphological variation in males of Dendrocephalus orientalis (Anostraca: Thamnocephalidae): Implications for species identification.

The genus Dendrocephalus Daday, 1908 consists of 17 described species. The morphology of the frontal appendage and the first pairs of thoracopods of males are the main characteristics used for species identification. The objectives of this study were to increase knowledge of the morphology of Dendrocephalus orientalis and to propose a new identification key for the species occurring in Brazil. Specimens were collected in temporary ponds within the conservation unit Monument Natural Grota do Angico (MNGA), which straddles the borders of the municipalities of Poço Redondo and Canindé de São Francisco, State of Sergipe, Brazil. During the study period, 560 male individuals of D. orientalis were sampled. The specimens showed variations in the number of spines on the eyes and the proximal surface of the male frontal appendage. On the eye, the number of spines ranged from 0 to 2; morphotypes with 1 and 2 spines predominated in the samples, with 50.5% and 46.2%, respectively. The number of spines on each eye was the same within each individual. On the proximal surface of the males frontal appendage the following numbers of spines on each arm were recorded: 1 and 1 (57.86%); 2 and 1 (30.89%); 2 and 2 (9.46%); 1 and 0 (1.25%); 3 and 2 (0.36%); 2 and 0 (0.18%). Based on these variations, we conclude that the number of spines on the eyes and the frontal appendage arms cannot be used as a diagnostic character for species identification. On the other hand, the first pairs of thoracopods and sub-branches 1V and 2A of the frontal appendage should be included in keys, since these structures did not show significant intraspecific morphological variation.