The Australian gulf snapping turtle Elseya lavarackorum (Testudines: Chelidae) revisited—Is the late Pleistocene fossil species extant?

Disagreement exists on the taxonomic identity of the extant populations of the Australian Elseya referred to in 1992 as the gulf Elseya (= Elseya sp. aff. dentata [Nicholson]). The extant form has since 1997 been considered conspecific with the late Pleistocene fossil Elseya lavarackorum (White and Archer, 1994). Recently it has been considered a new species, Elseya oneirosJoseph-Ouni et al., 2020, conspecific with another fossil found in the same site and stratum as Elseya lavarackorum. Here we re-examine the fossil material and reassess the characters used by previous authors in an attempt to decide the issue. We find that the anterior bridge suture with the carapace of the fossil Elseya lavarackorum is associated with extensive and prominent plastral elements, which has led to misinterpretation of characters associated with this structure. We furthermore show that interindividual variation in sulci patterns is so great as to render them of little taxonomic value. On the basis of (a) deviation of the anterior shape of the carapace from ovoid such that, in aged individuals, the most anterior point of the carapace occurs at marginal scutes M2 (a resultant nuchal bay occurs in such individuals); (b) the typical absence of a cervical scute; (c) no evidence of a medial constriction in the anterior bridge strut suture; and (d) absence of evidence of any other informative variation of taxonomic value; we conclude that the decision to consider the late Pleistocene (ca 23 kyr old) fossil and the extant Elseya sp. aff. dentata [Nicholson] as Elseya lavarackorum (White and Archer, 1994) as conspecific should stand.

Sex and male breeding state predict intraspecific trait variation in mouth-brooding fishes

Sex-specific reproductive roles contribute to sexual dimorphic morphological trait variations. In uniparental mouth-brooding fishes, the mouth performs a reproductive function in addition to its key roles in feeding and respiration, resulting in the potential for sex-specific functional performance trade-offs. Trait differences related to parental care may occur when the individual matures or be restricted to periods when the parent is mouth-brooding. This study explored sexual dimorphism and morphological trait adaptations related to feeding, breeding, respiration and locomotion performance in two paternal mouth-brooding freshwater fishes (Glossamia aprion and Neoarius graeffei). Eight morphological traits were evaluated for sexual dimorphism (non-brooder males vs. females) and male breeding state differences (brooders vs. non-brooders). Male breeding state was a significant predictor of trait variation in both species. Brooders differed in buccal volume and in several feeding and locomotory traits compared to non-brooder males. Non-brooder males had bigger buccal volumes and relative eye diameters (G. aprion) and larger relative gape sizes (N. graeffei) compared to females, a potential response to both mouth-brooding and feeding requirements. Although there were clear trait differences between brooder and non-brooder males, further research is required to confirm whether individuals return to their former morphology once mouth-brooding has ceased or if trait differences are maintained post-brooding. This study highlights the importance of considering the potential impacts of intraspecific trait variation on the performance of critical life functions, such as feeding, respiration and locomotion across the life history.

Diverse parentage relationships in paternal mouthbrooding fishes

While mouthbrooding is not an uncommon parental care strategy in fishes, paternal mouthbrooding only occurs in eight fish families and is little studied. The high cost of paternal mouthbrooding to the male implies a low risk of investment in another male's offspring but genetic parentage patterns are poorly known for paternal mouthbrooders. Here, we used single-nucleotide polymorphism genetic data to investigate parentage relationships of broods of two mouthbrooders of northern Australian rivers, mouth almighty Glossamia aprion and blue catfish Neoarius graeffei. For N. graeffei, we found that the parentage pattern was largely monogamous with the brooder male as the sire. For G. aprion, the parentage pattern was more heterogeneous including observations of monogamous broods with the brooder male as the sire (73%), polygyny (13%), cuckoldry (6%) and a brood genetically unrelated to the brooder male (6%). Findings demonstrate the potential for complex interrelationships of male care, paternity confidence and mating behaviour in mouthbrooding fishes.

Unravelling the taxonomy and identification of a problematic group of benthic fishes from tropical rivers (Gobiidae: Glossogobius)

Flathead gobies (genus Glossogobius) include c. 40 small- to medium-sized benthic fishes found primarily in freshwater habitats across the Indo-Pacific, having biodiversity value as well as cultural and economic value as food fishes, especially in developing countries. To help resolve considerable confusion regarding the identification of some of the larger-growing Glossogobius species, a systematic framework was established using nuclear genetic markers, mitochondrial DNA barcoding and phenotypic evidence for a geographically widespread collection of individuals from the waterways of tropical northern Australia. Species boundaries and distribution patterns were discordant with those previously reported, most notably for the tank goby Glossogobius giuris, which included a cryptic species. Genetic divergence was matched with accompanying unique visual characters that aid field identification. Additional taxonomic complexity was also evident, by comparison with DNA barcodes from international locations, suggesting that the specific names applicable for two of the candidate species in Australia remain unresolved due to confusion surrounding type specimens. Although flathead gobies are assumed to be widespread and common, this study demonstrates that unrealised taxonomic and ecological complexity is evident, and this will influence assessments of tropical biodiversity and species conservation. This study supports the need for taxonomic studies of freshwater fishes to underpin management in areas subject to significant environmental change.

Does a bigger mouth make you fatter? Linking intraspecific gape variability to body condition of a tropical predatory fish

In gape-limited predators, gape size restricts the maximum prey size a predator is capable to ingest. However, studies investigating the energetic consequences of this relationship remain scarce. In this study, we tested the hypothesis that gape-size variability influences individual body condition (a common proxy for fitness) in one of the largest freshwater teleost predators, the barramundi. We found that individual barramundi with larger gapes relative to body size had higher body condition values compared to conspecifics with smaller gapes. Body condition was highest soon after the wet season, a period of high feeding activity on productive inundated floodplains, and body condition decreased as the dry season progressed when fish were restricted to dry season remnant habitats. The increased condition obtained during the wet season apparently offsets weight loss through the dry season, as individuals with large gapes were still in better condition than fish with small gapes in the late-dry season. Elucidation of the links between intraspecific variability in traits and performance is a critical challenge in functional ecology. This study emphasizes that even small intraspecific variability in morphological trait values can potentially affect individual fitness within a species' distribution.

Larval nurseryfish, Kurtus gulliveri (Perciformes : Kurtidae), in the Adelaide River of the Northern Territory: their season, fellow travellers and unusual rib anatomy

This study was undertaken to determine the spawning season of the nurseryfish, a species with a unique method of parental care found only in northern Australia and southern New Guinea. Monthly samplings with an ichthyoplankton net at the same locality in the Adelaide River over multiple years yielded no larval nurseryfish in February, March, April and May. Larvae first appeared in June and were collected each month until January. From this we conclude that the nurseryfish spawning season in the Adelaide River is June–January. Twelve other larval fish species from 10 families were collected in the plankton tows with nurseryfish. Larval nurseryfish are readily identified and separated from other larval fishes by their peculiar rib anatomy, an important diagnostic character of Kurtus. The development of the unusual rib anatomy is examined with three-dimensional micro-computerised tomography scans of 12–21-mm standard length (SL) specimens. The bony protection of the swim bladder formed by the ribs is visible in the smallest postflexion specimens examined and is essentially complete by 19 mm SL. These ecological and anatomical observations add another pixel to the big picture of nurseryfish life history.

Reproductive anatomy, gonad development and spawning seasonality of nurseryfish, Kurtus gulliveri (Perciformes:Kurtidae)

The nurseryfish, Kurtus gulliveri, of northern Australia, is remarkable for the fact that the males carry the egg mass on a supraoccipital hook on their forehead. Plankton samples of larval nurseryfish indicate a prolonged spawning season (June–November) that more or less corresponds with the dry season in the Northern Territory. The paired, elongate testes are located in the posterior portion of the body cavity suspended by the mesorchium. The gonadosomatic index (GSI) of males was small and highly variable (mean 0.14, range 0.01–0.27) from June to November. The histological structure of testicular lobes showed maturing and mature stages that contained spermatocytes, spermatids, and spermatozoa. The paired, bean-shaped ovaries contained about 5500 oocytes (1176–9783) and were located in the rear of the abdominal cavity. GSI averaged 1.58 (range 0.36–4.48). Ovarian histology revealed primary growth, cortical alveolar oocytes, vitellogenic oocytes, coalesced yolk, and atresia. The occurrence of postovulatory follicles and late vitellogenetic oocytes in the ovaries clearly indicate that nurseryfish females are batch spawners. Maturing testes showed signs of previous spawnings indicating that males are capable of spawning several times throughout the spawning season. We speculate that nurseryfish may spawn in a manner similar to their closest relatives, cardinalfishes (Apogonidae), with eggs carried on the male’s hook instead of orally.

The bacterial mutagenicity of three naturally occurring indoles after reaction with nitrous acid

Three naturally occurring indoles were evaluated for potential nitrosatability using the Nitrosation Assay Procedure (NAP test) as recommended by the World Health Organisation. All three indoles i.e. tryptophan, tryptamine and 5-hydroxy-tryptamine were nitrosated to products which were directly mutagenic for S. typhimurium TA1537. In addition, the products of nitrosation of tryptamine and 5-hydroxytryptamine were also mutagenic for strains TA1538, TA98 and TA1535 without the need for metabolic activation. The sensitivities of the frameshift-detecting strains TA1537, TA1538 and TA98 were of particular interest, since nitroso compounds are characteristically base-substitution mutagens. The mutagenic effects of the products formed after nitrosation of each indole at pH 3.6, were eliminated in the presence of S9 mix. This was not the case when the nitrosation assay was carried out at pH 2.6. At this pH the mutagenicity of the nitrosated products varied in the presence of S9 mix and depended upon the nature of the indole undergoing nitrosation, and the bacterial test strain utilised for the mutagenicity assay. This indicated that more than one mutagenic product was responsible for the observed effects. As well as pH, a number of other factors influenced the formation of mutagenic nitroso products. Most notably, the concentrations of precursor compounds (sodium nitrite, and indole) present in the NAP test were of critical importance. As the sodium nitrite concentration was reduced from that recommended by the W.H.O. (40 mM), so the mutagenicity decreased. For all three compounds significant mutagenic effects were lost at sodium nitrite concentrations below 15 mM. In conclusion the data presented in this paper clearly demonstrates that individuals are chronically exposed to naturally occurring substances which readily nitrosate in excess nitrous acid and yield bacterial mutagens.