Epigenetics underpins phenotypic plasticity of protandrous sex change in fish

Phenotypic plasticity is an important driver of species resilience. Often mediated by epigenetic changes, phenotypic plasticity enables individual genotypes to express variable phenotypes in response to environmental change. Barramundi (Lates calcarifer) is a protandrous (male-first) sequential hermaphrodite that exhibit plasticity in length-at-sex change between geographic regions. This plasticity is likely to be mediated by changes in DNA methylation (DNAm), a well-studied epigenetic modification. However, region-specific relationships between length, sex and DNAm in sequential hermaphrodites were previously unreported. To investigate these relationships, here we compare DNAm in four conserved vertebrate sex-determining genes in male and female barramundi of differing lengths from three regions of northern Australia. Despite a strong association between increasing length and male-to-female sex change, the data reveal that DNAm becomes more sex-specific (rather than more female-specific) with length. Significant differences in DNAm between males and females of similar lengths suggest that female-specific DNAm arises rapidly during sex change, rather than gradually with growth. The findings also reveal that region-specific differences in length-at-sex change are accompanied by differences in DNAm, and were concurrent with variability in remotely sensed sea temperature and salinity. Together, these findings provide the first in situ evidence for epigenetically and environmentally mediated sex change in a protandrous hermaphrodite, and offer significant insight into the molecular and ecological processes governing the marked and unique plasticity of sex in fish.

The developmental variations of the sagitta otolith in the young and mature male of a hermaphrodite polynemidae fish, Eleutheronema tetradactylum (Shaw, 1804)

The Eleutheronema tetradactylum is a protandrous, hermaphrodite, marine perciformes fish. The body length of this fish acts as an important diagnostic marker for male and female discrimination. The present study describes for the first time the ultrastructural characteristics on the medial surface of the sagitta otolith in different body size groups of males of E. tetradactylum (Polynemidae: Perciformes) using scanning electron microscopy. The sagitta is a spindle-shaped structure that includes a well-developed rostrum and a poorly developed antirostrum. The sulcus is ostio-pseudocaudal type, almost straight and devoid of the collum. The ostium is a well-developed, vase-shaped structure. The cauda includes the colliculum and a well-developed caudal bulb with several distinct growth stripes. The length of the caudal bulb is significantly correlated to the growth of the body size of the fish. The excisura major is indistinct and the excisura minor is absent. The cristae are distinct on both sides of the sulcus. The one-way ANOVA test revealed that the development of several sagitta features shows significant differences in various body size groups of E. tetradactylum. The growth of the sagitta length is more closely related to the fork length than the sagitta width. Therefore, the sagitta length and the caudal bulb length can be used as important predictors to evaluate the fish size. The cauda region of the sagitta in E. tetradactylum is unique as well as more decorative than those of another Polynemidae fish and other hermaphrodite, marine perciformes fishes. The sagitta characteristics of E. tetradactylum might be advantageous in the identification of the sex and the taxonomy of the hermaphrodite fish species.

Reproductive Traits and Somatic Growth of Diplodus sargus sargus (Linnaeus, 1758) in the Central Algerian Coast (Southern Mediterranean Sea)

This work provides useful knowledge on the reproductive traits and somatic growth of the white seabream (Diplodus sargus sargus Linnaeus, 1758) of the central sector of the Algerian coast. It aimed to estimate the maximum yield size of this sparid and evaluate its reproductive potential, by presenting the first results on its global fecundity. A total of 497 specimens, ranging in size from 12.4 to 40.3 cm, were monthly and randomly sampled from the artisanal fishery fleet, between January and December 2017. The obtained length-weight relationships indicated negative allometry for males (TW=0.024 TL2.842) and isometry for females (TW=0.016 TL3.013). The white seabream is a digynic protandrous hermaphrodite species. Sex reversal was observed with a large size overlap of 12 to 32 cm with a median of 23.5 cm. The reproductive season was observed from January to May and spawning occurred in spring. The size at first sexual maturity (TL50) was 20.55 cm for both sexes. Based on these results, the current legal minimum size of capture should be raised in the study area.

Faster juvenile growth promotes earlier sex change in a protandrous hermaphrodite (barramundi Lates calcarifer)

The relationship between growth and sexual maturation is central to understanding the dynamics of animal populations which exhibit indeterminate growth. In sequential hermaphrodites, which undergo post-maturation sex change, the size and age at which sex change occurs directly affects reproductive output and hence population productivity. However, these traits are often labile, and may be strongly influenced by heterogenous growth and mortality rates. We analysed otolith microstructure of a protandrous (i.e., male-to-female) fish (barramundi Lates calcarifer) to examine growth in relation to individual variation in the timing of sex change. Growth trajectories of individuals with contrasting life histories were examined to elucidate the direction and extent to which growth rate influences the size and age individuals change sex. Then, the relationships between growth rate, maturation schedules and asymptotic maximum size were explored to identify potential trade-offs between age at female maturity and growth potential. Rapid growth was strongly associated with decreased age at sex change, but this was not accompanied by a decrease in size at sex change. Individuals that were caught as large females grew faster than those caught as males, suggesting that fast-growing individuals ultimately obtain higher fitness and therefore make a disproportionate contribution to population fecundity. These results indicate that individual-level variation in maturation schedules is not reflective of trade-offs between growth and reproduction. Rather, we suggest that conditions experienced during the juvenile phase are likely to be a key determinant of post-maturation fitness. These findings highlight the vulnerability of sex-changing species to future environmental change and harvest.

TIPE PERIKANAN DAN STATUS SUMBERDAYA IKAN TERUBUK (Tenualosa macrura, Bleeker 1852), DI PERAIRAN ESTUARIN BENGKALIS DAN SELAT PANJANG

Ikan terubuk (Tenualosa spp.) adalah ikan estuarin bersifat ‘protandrous hermaphrodite’ dan endemik di estuarin sekitar Bengkalis. Jenis Tenualosa macrura ditemukan di sekitar Bengkalis (Riau), jenis T. ilisha di sekitar Labuhan Batu dan Labuhan Bilik (Sumatra Utara), sedangkan T. toli ditemukan di perairan pantai barat Pemangkat (Kalbar). Sumber daya terubuk di sekitar Bengkalis saat ini sangat menurun akibat eksploitasi dan recruitment overfishing meskipun pembatasan penangkapan telah diterapkan. Tulisan ini membahas status sumber daya ikan terubuk di sekitar Bengkalis dan Selat Panjang berdasarkan data monitoring hasil tangkapan periode 2014-2016 dan observasi lapangan selama 2015-2016. Ikan terubuk merupakan ikan dominan dari enam jenis hasil tangkapan pada gill net, jumlahnya sekitar 15% dari total hasil tangkapan, upaya penangkapan tergolong intensif sehingga penurunan upaya yang dilakukan ternyata kurang signifikan, bahkan pada saat close season dan close area (September sampai November) upaya penangkapan cenderung tinggi. Kondisi ini tentu tidak sesuai dengan tujuan perlindungan terbatas dan konservasi jenis yang diterapkan. Penurunan populasi terubuk tampak nyata dalam bentuk hasil tangkapan (CPUE), sex ratio maupun produksi pendaratan. Ikan kategori “Pias” (ikan jantan) tetap dominan dan semakin banyak, sebaliknya kategori “Terubuk” (ikan betina matang gonad) semakin sedikit, artinya ukuran rata-rata ikan juga semakin kecil. Keberadaan populasi ikan terubuk di sekitar P. Tiga (Kab. Kepulauan Meranti) dengan kondisi matang gonad dan secara genetik memiliki pola DNA yang sama dengan yang berada di Bengkalis. Perluasan daerah konservasi dan perlindungan terbatas terhadap stok-stok tersebut disarankan.The terubuk (Tenualosa spp) or shads, is a estuarine and endemic ‘protandrous hermaphrodite’ fish species. Species Tenualosa macrura is found in estuarine waters around Bengkalis (Riau Province), T. ilisha around Labuhan Batu and Labuhan Bilik (North Sumatera Province) while T. toli in west coast of Pemangkat (West Kalimantan Province). The terubuk reosurce in Bengkalis water is heavily degraded due to high exploitation and recruitment overfishing eventhough fishing limitation is applied. This paper is discussing the status of terubuk/longtail shad (Tenualosa macrura) resources in Bengkalis estuarine and Selat Panjang waters (Kabupaten Kepulauan Meranti) base on data of 2014-2016 catch monitoring data and field observation during 2015-2016. Terubuk is one of 6 dominant catches from gillnet, contributing about 15% of all catch. The fishing effort was so intensive even though management measure is applied to reduce its exploitation. During the close season when fishing on terubuk is banned (in September to November) as well as the ban in close area , the fishing effort has been still high. This condition is not in line with the objective of protecting the terubuk resources. Therefore, this condition must be changed and returned to objective of “limited protection” and “species conservation” by adopting a more strict rule on limiting fishing effort on terubuk through an evaluation. The decreasing of terubuk population can be seen from CPUE, sex ratio and also in landing, short time (2012 – 2016) and long time (18 years). In overall, the “Pias” (adult male) individuals remainned dominant and wereeven getting more in number, while the “Terubuk” (adult female) on the contrary, which means that the average size of actual fish cought was getting smaller. The existence of terubuk population around Pulau Tiga (Kabupaten Kepulauan Meranti) with mature gonad would share the same genetic pattern with population from Bengkalis. This explaines the connectivity between two stocks, at least there might be another spawning stock other than Bengkalis’s. The expand of the conservation area and limited protection on those stocks is highly recommended.

Microstomum (Platyhelminthes, Macrostomorpha, Microstomidae) from the Swedish west coast: two new species and a population description

Two new species of marine Platyhelminthes, Microstomum laurae sp. nov. and Microstomum edmondi sp. nov. (Macrostomida: Microstomidae) are described from the west coast of Sweden. Microstomum laurae sp. nov. is distinguished by the following combination of characters: rounded anterior and posterior ends; presence of approximately 20 adhesive papillae on the posterior rim; paired lateral red eyespots located level with the brain; preoral gut extending anterior to brain and very small sensory pits. Microstomum edmondi sp. nov. is a protandrous hermaphrodite with a single ovary, single testis and male copulatory organ with stylet. It is characterized by a conical pointed anterior end, a blunt posterior end with numerous adhesive papillae along the rim, and large ciliary pits. The stylet is shaped as a narrow funnel with a short, arched tip. In addition, the first records of fully mature specimens of Microstomum rubromaculatum von Graff, 1882 from Fiskebäckskil and a phylogenetic analysis of Microstomum Schmidt, 1848 based on the mitochondrial cytochrome oxidase I (COI) gene are presented.