Samara de Paiva Barros-Alves

Context: Understanding the processes that influence species diversity and distribution is a central goal in ecology. Aims: This study investigated the global distribution of freshwater shrimps in the genus Macrobrachium and evaluated the environmental and historical factors driving their species richness across biogeographic realms. Methods: We analysed predictive models composed of multiple environmental predictors across biogeographic regions, testing which hypothesis (temperature–speciation, water–energy and habitat heterogeneity) or a combination of hypotheses best explains species richness. Key results: Our analyses showed that the highest Macrobrachium species richness occurs in the Neotropic and Indo-Malay realms. The best model varied among regions, reflecting regional differences and the historical influences: Afrotropic and Australasia shared similar models, as did Neotropical and Palearctic regions. Indo-Malay exhibited a distinct model, with variations in the most influential variables according to local conditions. Conclusion: These findings suggest that combined environmental and historical factors are key predictors of Macrobrachium species richness. Implications: This study underscores the importance of integrating environmental and historical factors when assessing species richness patterns and offers a scientific basis for conservation strategies. It highlights the need to consider current environmental changes when protecting biodiversity hotspots and the diversity of Macrobrachium across freshwater ecosystems.

Aim: We studied the niche evolution and diversification modes in transisthmian Alpheus shrimps by examining the interplay between environmental niche divergence and conservatism in allopatric sister species. In a broader perspective, the current study analysed the evolution of climatic niche and the role of the environment in species diversification of Alpheus transisthmian shrimp. Location: Atlantic and Eastern‐Pacific oceans. Taxon: Alpheus shrimps (Caridea: Alpheidae). Methods: We assembled georeferenced occurrences for 33 species of Alpheus (with 24 sister species) from a time‐calibrated molecular phylogeny. We modelled their ecological niches and assessed niche overlap through pairwise comparisons. Additionally, we performed phylogenetic reconstructions of the ancestral environmental niche, for each niche axis. Results: Our results demonstrate that thermal tolerances, food availability and hydrodynamic forces were relevant environmental axes in evolutionary processes in transisthmian species of Alpheus . Among the 528 paired comparisons, we found that most niches were divergent, including in 12 clades formed by pairs of sister species (in only two of these clades were the niches fully equivalent). Phylogenetic reconstructions of ancestral niches showed an initial niche conservatism in all axes, with divergences intensifying in the last 12 million years. Main Conclusions: We found evidence that confirms the relevance of the environmental changes that occurred in the West Atlantic and East Pacific for niche evolution in transisthmian Alpheus species, as well as for the emergence of some lineages. Our findings provide evidence for different modes of Alpheus species speciation in a period consistent with the closure of the Isthmus of Panama.

The evaluation of the effects of early starvation and feeding on survival and growth in the early stages of the life cycle of ornamental marine caridean shrimp species is fundamental to establish adequate feeding protocols in their culture. In this study, we determine the nutritional vulnerability in the early larval stages of ornamental shrimp Lysmata ankeri exposed to different periods of starvation or feeding. The larvae were separated into three groups (zoea I-ZI, zoea II with ZI fed, and zoea II with ZI unfed) and subjected to two experiments: (1) point-of-no-return (PNR), comprising one or two days of initial starvation followed by feeding; and (2) point-of-reserve-saturation (PRS), comprising one or two days of initial feeding followed by starvation. Each experiment was still composed of two control groups: continuous feeding and continuous starvation. Larvae tolerated some periods of starvation, with a high PNR value (2.00) and low PRS (0.50). Longer periods of starvation influenced both growth and survival rates in zoea II stages. The nutritional vulnerability index for zoea I was 0.25, which represents a low dependence on food supply. In this study, it was observed that ornamental shrimp L. ankeri larvae hatch with energy reserves, presenting facultative primary lecithotrophy, in which they are able to moult from zoea I to zoea II using such reserves in the absence of food. In this sense, the early larvae stages (zoeas I and II) can tolerate a certain period of starvation, indicating the great potential of this species for aquaculture.

Brazil contains about 5% (~120 spp.) of the total known species of freshwater decapods. Information on the occurrence of freshwater decapod species in the state of Minas Gerais is dispersed and much of this remains unpublished. We hereby propose to present the first inventory of freshwater decapods from the state, based on data compiled from publications and scientific collections and obtained from fieldwork in the state. Eleven species of freshwater decapods were recorded in Minas Gerais, including three species of crabs (Trichodactylidae), seven of shrimps (Palaemonidae) and one species of freshwater squat lobster (Aeglidae), classified into three infraorders, three families, and four genera. The genus Macrobrachium C.S. Bate, 1868 comprised most of the decapod records. The reduced number of species in relation to coastal states is related, at least in part, to the absence of amphidromic species. Environmental degradation and the construction of dams in several watersheds may be possible causes of this absence. The records obtained from surveys carried out in national parks situated in Minas Gerais and its surroundings indicate the importance of these areas for the conservation of decapod fauna in the state.

The early larval stages of the shrimps Lysmata ankeri and L. bahia were described, illustrated, and compared among other Lysmata species, providing important information on post-embryonic development and insights into its evolutionary history. Ovigerous specimens of L. ankeri and L. bahia were sampled from southeastern and northeastern Brazilian coast, respectively. For L. ankeri and L. bahia, five and three larval stages were obtained, respectively. Unique features were observed for L. ankeri and L. bahia larvae, and some characteristics may differ only for L. ankeri and L. bahia, which were not observed in the other species analyzed, such as: presence of a pair of simple setae on the third pleonal somite in zoea I and number of setae on the uropod exopod greater than 11. Moreover, several other features are similar between species from the diferent clades of the Lysmata-Exhippolysmata complex, making it possible to identify the early stages of Lysmata larvae. However, future studies will be essential to confirm or not the existence of some phylogenetic patterns and their relevance and other larval characters for better understanding the evolutionary history of this group.

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.

Growth and longevity parameters of males and females of Macrobrachium brasiliense were analyzed. Samplingwas carried out monthly from July 2012 to June 2013 in Triângulo Mineiro region, Minas Gerais, Brazil. A total of199 adult prawns (97 males and 102 females) were analyzed and measured according to the carapace length (CL, mm). Males (9.64 ± 4.17 mm, CL) were larger than females (7.7 ± 3.39 mm, CL). CL growth curves by the von Bertalanffy model are described by the equations CL = 21.0 [1 - e -0.00446 (t)] for males and CL = 20.0 [1 - e -0.00454 (t)] for females. Comparison of the growth curves by performing the F-type test, showed that there was no differencebetween the growth coefficients (K) of males and females (GL22; F3.16 = 2.476; p = 0.088). Longevity was estimated as 2.83 years for males and 2.78 years for females. In general, the observed longevity is similar to that of other Macrobrachium species.