Extreme secondary sexual dimorphism in the genus Florarctus (Heterotardigrada: Halechiniscidae)

Secondary sexual dimorphism in florarctin tardigrades is a well-known phenomenon. Males are usually smaller than females, and primary clavae are relatively longer in the former. A new species Florarctus bellahelenae, collected from subtidal coralline sand just behind the reef fringe of Long Island, Chesterfield Reefs (Pacific Ocean), exhibits extreme secondary dimorphism. Males have developed primary clavae that are much thicker and three times longer than those present in females. Furthermore, the male primary clavae have an accordion-like outer structure, whereas primary clavae are smooth in females. Other species of Florarctus Delamare-Deboutteville & Renaud-Mornant, 1965 inhabiting the Pacific Ocean were investigated. Males are typically smaller than females, but males of Florarctus heimi Delamare-Deboutteville & Renaud-Mornant, 1965 and females of Florarctus cervinus Renaud-Mornant, 1987 have never been recorded. The Renaud-Mornant collection was re-examined, and type series were analysed. Florarctus heimi and F. cervinus were always found together in the coralline sand of Heron Island (Great Barrier Reef). The animals were kept alive and surveyed in the laboratory of the Queensland Museum. All studied individuals of the larger F. heimi (up to ca. 400 μm) were females, and all adults of the smaller F. cervinus (about 170 μm) were males. Males of F. cervinus were observed mating with females of F. heimi. Following those morphological and behavioural lines of evidence, we propose that F. cervinus is a junior synonym of F. heimi. Based on the discovery of dimorphism in F. bellahelenae sp. nov. and the strong sex-related morphological disparities in F. heimi, we suggest that extreme secondary dimorphism may be present in other florarctin arthrotardigrades.

Rich but not poor conditions determine sex‐specific differences in growth rate of juvenile dioecious plants

Causes of secondary sexual dimorphism (SSD) in dioecious plants are very poorly understood, especially in woody plants. SSD is shown mainly in mature plants, but little is known about whether secondary sexual dimorphism can occur in juveniles. It is also assumed that stress conditions intensify differences between the sexes due to the uneven reproductive effort. Therefore, the following research hypotheses were tested: (1) secondary sexual dimorphism will be visible in juveniles; (2) unfavourable soil conditions are the cause of more pronounced differences between the sexes. Rooted shoots of the common yew (Taxus baccata L.) and common juniper (Juniperus communis L.), previously harvested from parental individuals of known sex were used in the study. During two growing seasons vegetation periods and four times a year, comprehensive morphological features of whole plants were measured. Some SSD traits were visible in the analysed juveniles. Contrary to expectations, differences were more pronounced in the fertilized treatment. Both species reacted to fertilization in different ways. Female yew had a clearly higher total plant mass, root mass, and mean root area when fertilized, whereas male juniper had a higher root mass when fertilized. Differences between the sexes independent of the fertilization treatment were seen, which can be interpreted as sexual adaptations to a continued reproduction. Female yews and male junipers made better use of fertile habitats. Our study showed that SSD may be innate, and sexual compensatory mechanisms could generate uneven growth and development of both sexes. Because the SSD pattern was rather different in both species, it was confirmed that SSD is connected with the specific life histories of specific species rather than a universal strategy of dioecious species.

The genetic basis of sex determination in Populus provides molecular markers across the genus and indicates convergent evolution

Many dioecious angiosperms are trees, which only flower after years of vegetative development and do not usually exhibit marked secondary sexual dimorphism. Nevertheless, if the genetic basis of sex determination is known, the sex of an individual can be determined using molecular markers. Here, we report that in the genus Populus sect. Populus an XY system of sex determination, which is found in P. tremula and P. tremuloides, likely re-evolved from a ZW system present in P. alba, P. adenopoda and P. qiongdaoensis. Strikingly, this new XY system is mechanistically identical to the older system found in several species of the Populus sections Tacamahaca, Aigeiros and Turanga demonstrating a remarkable example of convergent evolution. In both XY systems, male-specific inversely repeated sequences appear to silence the ARR17 gene, which functions as a sex switch, via small interfering RNAs and DNA methylation. In the ZW system, female-specific copies of ARR17 appear to regulate dioecy. With this detailed information on the genetic basis of sex determination it was possible to develop molecular markers that can be utilized to determine the sex in seedlings and non-flowering trees of different poplar species. We used the female-specific ARR17 gene to develop a sex marker for P. alba and P. adenopoda. For P. grandidentata, we employed the male-specific ARR17 inverted repeat. Finally, we summarize previously described markers for P. tremula, P. tremuloides, P. trichocarpa, P. deltoides and P. nigra. These markers can be useful for poplar ecologists, geneticists and breeders.

A redescription of deep-channel ghost knifefish, Sternarchogiton preto (Gymnotiformes: Apteronotidae), with assignment to a new genus

ABSTRACT From a study of morphological and molecular datasets we determine that a species originally described as Sternarchogiton preto does not form a monophyletic group with the other valid species of Sternarchogiton including the type species, S. nattereri. Previously-published phylogenetic analyses indicate that this species is sister to a diverse clade comprised of six described apteronotid genera. We therefore place it into a new genus diagnosed by the presence of three cranial fontanels, first and second infraorbital bones independent (not fused), the absence of an ascending process on the endopterygoid, and dark brown to black pigments over the body surface and fins membranes. We additionally provide a redescription of this enigmatic species with an emphasis on its osteology, and provide the first documentation of secondary sexual dimorphism in this species.

Reassignment of 'Triplophysa' jiarongensis (Cypriniformes: Nemacheilidae) to Oreonectes Günther, 1868

Specimens identified as Oreonectes jiarongensis (Cypriniformes: Nemacheilidae) were collected from a karst cave in Jiarong Town and Banzhai Township, Libo County, Guizhou, China. Several lines of morphological and molecular evidence suggested that this species was similar to species of Oreonectes Günther 1868 and not closely related to species of Triplophysa Rendal, 1933. The anterior and posterior nostrils of 'Triplophysa' jiarongensis were separated by a short distance, and there was no secondary sexual dimorphism in male specimens. The Bayesian phylogenetic analysis based on cytochrome b recovered 'T.' jiarongensis in a well-supported clade with Oreonectes daqikongensis, O. shuilongensis, O. furcocaudalis and O. platycephalus, sister to the Triplophysa clade. In addition, the genetic distances between 'T.' jiarongensis and species of Oreonectes were low (O. daqikongensis: 0.114; O. shuilongensis: 0.106; O. platycephalus: 0.180), while distances to species of Triplophysa were higher (T. dorsalis: 0.233; T. yarkandensis: 0.282). Therefore, we reassign 'T.' jiarongensis to Oreonectes. Based on this result, it is now clear that species of both Oreonectes and Triplophysa inhabit the same underground river system in Guizhou. However, as species of Oreonectes are only known from the southern part of Guizhou, it may be that O. jiarongensis inhabits the most northerly part of the range of this genus.

Amazonopsis, an unusual new genus of riffle beetle from South America with two new species (Coleoptera, Elmidae, Elminae)

Amazonopsisgen. n.is described to includeA.theranyisp. n.from Peru, Venezuela and French Guiana, andA.camachoisp. n.from Venezuela. The descriptions are accompanied by figures illustrating the male and female habitus ofA.theranyi, the male habitus ofA.camachoi, and male genitalia of both species.Amazonopsistheranyiexhibits pronounced secondary sexual dimorphism which likewise may be a characteristic of the genus.Amazonopsismales have modified protarsal and mesotarsal claws, a pair of small spines on the anterior prosternum, and a pair of ventrally directed processes on the posterior metaventrite. Females ofA.theranyidisplay a pair of unique, oval perforations in the cuticle of the pronotum and have unmodified claws; females ofA.camachoiare unknown. Descriptions are furnished of the stream habitats and microhabitats where the study specimens were collected.