Nibia Berois

Annual fish: developmental adaptations for an extreme environment

Annual fish are freshwater teleosts found in South America and Africa that are exposed to an extremely variable environment. They develop and reproduce in seasonal ponds that dry during the summer eliminating the entire adult population. Remarkably, desiccation‐resistant embryos survive in these dry ponds that hatch during the next rainy season when the ponds are recreated. Among vertebrates, they represent one of the most remarkable extremophiles. They share several features with other fish models; however, they exhibit unique traits related to their peculiar life cycle. Epiboly is temporally and spatially uncoupled from organogenesis, and the embryos can undergo reversible developmental arrests (diapauses). These attributes make them a useful model to study diverse topics in developmental biology using a comparative and evolutionary approach. In this article, different aspects related to annual fish biology, taxonomy and phylogenetic considerations, reproductive strategy, and developmental characteristics with special focus on arrests, are summarized. The current challenge is to document and determine the factors that generate such high diversity and unique adaptations of annual fish. To understand this complexity, interdisciplinary approaches are being employed taking into consideration evolutionary biology, ethology, reproductive strategies, regulation of developmental mechanisms, and senescence. WIREs Dev Biol 2012, 1:595–602. doi: 10.1002/wdev.39

Gamete interactions in teleost fish: the egg envelope. Basic studies and perspectives as environmental biomonitor

The current knowledge about teleost fish egg envelope is summarized. The paper analyzes the organization and deposition process of the protein composition and genes involved in the synthesis of teleost fish egg envelopes and their role in gamete interaction during fertilization. Pelagic and demersal species that our research group is working with are especially considered. The vertebrate ZP family of proteins, the evolution and relationship among the different genes and their expression are taken into account. We consider fish envelope as a possible biomonitor for ecological contaminants. The biotechnological applications for aquaculture and genomic and post-genomic approaches are auspicious.

Histology of the Ovaries and Fat Bodies of Chthonerpeton indistinctum

Histological analysis revealed three different stages in the development of ovarian follicles of Chthonerpeton indistinctum. These stages are identified by (1) location of the oocyte in the ovary wall, (2) oocyte morphology and staining characteristics, (3) development of the zona pellucida, and (4) orga- nization of the follicular layer. Atretic follicles and corpora lutea also were found. Fat bodies are composed of well-developed adipose tissue. The caecilian family Typhlonectidae in- cludes 19 aquatic, viviparous species. Aside from Taylors monograph on Gymno- phiona (1968) and the work done on Typh- lonectes compressicauda by Exbrayat (1983), Exbrayat and Collenot (1983), Exbrayat et al. (1981, 1982) and Delsol et al. (1981), little information is available on the re- productive biology of this family. Lieber- man (1939) and Barrio (1969) described some aspects of the reproductive behavior of Chthonerpeton indistinctum (Reinhardt and Lutken, 1862). Histological aspects of the oviducts of this species were studied by Welsch et al. (1977), and de Sa and Berois (1986) studied the spermatogenesis. Ovar- ian morphology and histology were de- scribed by Wake (1968, 1977) for several species of caecilians, but histological data for Chthonerpeton were not included. Clas- sification of ovarian eggs in caecilians has been based on egg sizes (Wake, 1977; Ex- brayat and Collenot, 1983). Review papers dealing with the ovary of nonmammalian vertebrates, such as those in the volume by Jones (1978) and Wallace (1983), base their presentations on the am- phibian ovary from work done on anurans or urodeles only. In this paper, we present a histological analysis of the ovary and fat bodies of C. indistinctum. It was found that

Spermatogenesis and Histology of the Testes of the Caecilian, Chthonerpeton indistinctum

Macroscopically, the testes of Chthonerpeton indistinctum consist of a series of oval lobes. The number and size of lobes is variable in Chthonerpeton indistinctum. Histologically, the testes are divided into structural units, locules separated by septa of connective tissue. Inside of each locule spermatogenesis takes place in cysts of germinal cells that divide synchronically. Sper- miogenesis is divided chronologically into four stages of development based on the shape of the nuclei of the spermatids and their arrangement in the cyst: (1) round, (2) kidney shaped, (3) atten- uate, and (4) bouquet arrangement.

The Neotropical Genus Austrolebias: An Emerging Model of Annual Killifishes

Annual fishes are found in both Africa and South America occupying ephemeral ponds that dried seasonally. Neotropical annual fishes are members of the family Rivulidae that consist of both annual and non-annual fishes. Annual species are characterized by a prolonged embryonic development and a relatively short adult life. Males and females show striking sexual dimorphisms, complex courtship, and mating behaviors. The prolonged embryonic stage has several traits including embryos that are resistant to desiccation and undergo up to three reversible developmental arrests until hatching. These unique developmental adaptations are closely related to the annual fish life cycle and are the key to the survival of the species. Most of the available data on Neotropical annual fishes derive from studies on the genus Austrolebias. Herein, we review and summarize the available data on the evolution, reproduction strategy, developmental biology and conservation status of these Neotropical fishes.

Sex determination in annual fishes: searching for the master sex-determining gene in Austrolebias charrua (Cyprinodontiformes, Rivulidae)

Evolution of sex determination and differentiation in fishes involves a broad range of sex strategies (hermaphroditism, gonochorism, unisexuality, environmental and genetic sex determination). Annual fishes inhabit temporary ponds that dry out during the dry season when adults die. The embryos exhibit an atypical developmental pattern and remain buried in the bottom mud until the next rainy season. To elucidate genomic factors involved in the sex determination in annual fish, we explored the presence of a candidate sex-specific gene related to the cascade network in Austrolebias charrua. All phylogenetic analyses showed a high posterior probability of occurrence for a clade integrated by nuclear sequences (aprox. 900 bp) from both adults (male and female), with partial cDNA fragments of A. charrua from juveniles (male) and the dsx D. melanogaster gene. The expressed fragment was detected from blastula to adulthood stages showing a sexually dimorphic expression pattern. The isolated cDNA sequence is clearly related to dsx D. melanogaster gene and might be located near the top of the sex determination cascade in this species.

A global community effort to decipher the unique biology of annual killifish: Global Network of Killifish Researchers

Over the past 50 years, annual killifishes arose as alternative model organisms for studies of vertebrate biology. The annual fish offers exceptional advantages for studies of genetics, genomics, developmental biology, population dynamics, ecology, biogeography, and evolution. They inhabit extremely variable freshwater environments in Africa and South America, have a short lifespan and a set of unique and fascinating developmental characteristics. Embryos survive within the dry substrate during the dry season, whereas the adult population dies. Thus, the survival of the populations is entirely dependent on the buried embryos that hatch the next rainy season. Although Old and New World species share similarities in their life cycle, they also have different adaptive responses associated with climate‐related selective pressures. Therefore, contrasting different species from these areas is essential to understand unique adaptations to heterogeneous environment. A network of laboratories (United States, Czech Republic, Italy, Brazil, Chile, and Uruguay) is working and collaborating on many aspects of the biology of annual fishes. Participating researchers share projects and cross‐training undergraduate and graduate students. These efforts resulted in two International Symposia (2010 and 2015) that took place in Montevideo and an international book. Herein, we summarize the progress made by this global community of scientists. Developmental Dynamics 246:807–811, 2017.

Annual killifish adaptations to ephemeral environments: Diapause i in two austrolebias species

Background: Many organisms are able to survive in extreme environments by entering a state of dormancy. In dormancy, vital activities are reduced until environmental conditions are compatible with active life. Annual killifishes show a special developmental pattern characterized by a phase of dispersion‐reaggregation of the blastomeres that separates epiboly from organogenesis, and the capability to enter dormancy in diapause. High tolerance to environmental stress confers annual killifish embryos the condition of extremophiles. At present, the questions of our research group are focused on the understanding of the mechanisms involved in diapause regulation through an interdisciplinary approach. As a first step, it is necessary to characterize diapauses at morphological and physiological levels and to evaluate induction cues under laboratory conditions. In this context, we characterized diapause I in two Austrolebias species. Results: Our experimental approach to induce diapause I was successful and revealed the co‐existence of two diapause I phenotypes named A and B instead of one. These phenotypes showed a tendency for lower total extractable RNA content compared with active developmental stages (80–100% epiboly and early reaggregate). Conclusions: These phenotypes are alternative diapause I stages and may have ecological relevance because both were found in embryos in natural ponds. Developmental Dynamics 246:848–857, 2017.