Frogs with denser group-spawning mature later and live longer

The understanding of the intrinsic and extrinsic causes of longevity variation has deservedly received much attention in evolutionary ecologist. Here we tested the association between longevity and spawning-site groups across 38 species of Chinese anurans. As indicators of group-spawning we used spawning-site group size and spawning-site density, which we measured at 152 spawning sites in the field. We found that both spawning-site density and group size were positively associated with longevity. Male group-spawning (e.g., male spawning-site density and male spawning-site group size) was also positively correlated with longevity. A phylogenetic path analysis further revealed that longevity seems directly associated with spawning-site density and group size, and that the association in part depend on the ‘groups-spawning-age at first reproduction’ association. Our findings suggest that the increased group-spawning are likely to benefit in declining extrinsic mortality rates and living longer through improving total anti-predator behaviour under predation pressure.

Altitudinal variation in male reproductive investment in a polyandrous frog species (Hyla gongshanensis jingdongensis)

Competition for fertilization in multi-male group spawning can drive variation in male reproductive investment (i.e., testis mass and sperm size). Inter-population comparisons of variation in energetic availability and allocation along geographical gradients allow insights into the mechanisms shaping the reproductive investments of animals. Although inter-population differences in female reproductive investment (i.e., clutch size and egg size) have been studied extensively across a wide range of taxa, little information on variation in reproductive investment in males is available. Here, we studied altitudinal variation in testis mass and sperm length among three populations in the Jingdong tree frog (Hyla gongshanensis jingdongensis), a polyandrous species, in Yunnan Province in China. The results showed that individuals exhibited smaller testes at higher altitudes while testes mass was positively correlated with body size, body condition and age. Longer sperm length was observed in the middle-altitude population. Moreover, we found that sperm number was positively correlated with testes mass and sperm length. Our correlational findings suggest that environmental constraints at high altitude select for less investment in testes and offspring number.

Spawning ascent durations of pelagic spawning reef fishes

Predation risks have been hypothesized to influence spawning behaviors of coral reef fishes that broadcast gametes pelagically. The duration of spawning ascents of 13 species were measured from video footage at a single spawning site for multiple coral reef fishes to investigate if this behavior was influenced by varying risks of predation. Fishes that spawned in pairs had ascents of longer duration than group-spawning species. Duration of spawning ascents did not vary between fishes spawning at daytime and dusk, nor between group-spawning species with specific anti-predatory morphological adaptations. These results indicate that risk of predation may not significantly influence the duration of spawning ascents of pair spawning reef fishes at our study site, while group-spawning behaviors are influenced by predation. Avoidance of egg predation by benthic organisms and female mate choice are more likely to influence the pelagic spawning behaviors of all fishes observed.

Sexual development and reproductive pattern of the Mutton hamlet, Alphestes afer (Teleostei: Epinephelidae): a dyandric, hermaphroditic reef fish

There is little knowledge on the reproduction of the genus Alphestes. The reproduction of the Mutton hamlet, Alphestes afer, sampled in Pernambuco reefs (Brazil) was studied based on macroscopic analysis during reproductive period and histological analysis of gonad material from March 2008 to October 2009. This study showed that A. afer is a diandric, protogynous hermaphrodite. Sex change followed protogynous mode in two pathways: primary males formed from immature female individuals or secondary males formed from resting, ripe or spent female individuals. The numerical distribution of gonad classes by size indicated that females from 11-18 cm L T were immature while females from 16-25 cm L T and males from 12-22 cm L T were in various stages of gonadal development. Individuals identified as immature bisexual and transitional (presenting both ovarian and sperm tissue) were sized from 16-24 cm L T. Size of first reproduction for females was 18 cm L T and for males was 12 cm L T. Alphestes afer showed multiple spawning, with spawning season period from August to December 2008 and from August to October 2009. The sex-ratio (females: males) in 2008 and 2009 was 0.94:1 during the months of spawning season. Males were smaller than females, reaching maximum size of 22 cm compared to 25 cm observed for females. Males showed a high sperm competition rank (3.8), suggesting intense sperm competition. This latter is a possible indication of a shift in the mating group structure from paired to group spawning. The presence of small males added to high sperm competition index, suggest that this species, while retaining the protogynous pattern, has a reproductive strategy similar to gonochorist epinephelids.

Mating behaviour of the newly-established ornate wrasse Thalassomapavo (Osteichthyes: Labridae) in the Ligurian Sea (north-western Mediterranean)

Reproduction of newly established populations of the warm-water Atlantic Mediterranean wrasse Thalassoma pavo is here reported for the first time in the Ligurian Sea, and mating behaviour is described in detail. The reproductive season (May to October) may be divided in three stages: (1) pre-mating (mid-May to the end of June), during which terminal-phase (TP) males establish territories and start courting females; (2) mating (end of June to the end of August), with a mean frequency of up to one spawning event ind−1 h−1; and (3) post-mating (September to mid-October), when TP males remained inside territories but no spawning events were recorded. Mating followed two distinct modalities: pair spawning and group spawning, the latter replacing the former when population density exceeded 10 ind 100 m−2. Four phases have been distinguished in both modalities: (1) approach (pair) or gathering (group), to establish the contact between potential partners; (2) acceptance (pair) or priming (group), in which partners establish a common behavioural pattern; (3) ascent to near the sea surface; and (4) spawning. The saddled sea-bream Oblada melanura has been seen to predate intensively on the large cloud of sexual products released by groups.