Testis size depends on social status and the presence of male helpers in the cooperatively breeding cichlid Julidochromis ornatus

Cooperatively breeding animals, in which helpers may participate in reproduction with dominant breeders, are ideal species for examining intraspecific variation in testis size because they often exhibit both monogamous breeding (low risk of sperm competition) and polyandrous breeding (high risk) within a population. However, little is known about testis investment as a result of sperm competition in these animals. The substrate-brooding cichlid fish Julidochromis ornatus has a cooperatively breeding system, in which some males mate monogamously and other males reproduce as dominant breeders or helpers within cooperatively breeding groups, in which male helpers frequently sire young. We examined the relationship between testis investment and male social status in relation to the risk of sperm competition. As predicted from sperm competition models, in groups with male helpers, both the male breeders and the male helpers invested more in testes mass, compared to breeding males without male helpers. We also found a positive relationship between the testes mass of male breeders and their male helpers, suggesting that males increase their investment in reproductive capability under the risk of sperm competition. Sperm competition models also predict that larger testes are associated with increased siring success. Our paternity analysis supported this prediction; we found a positive relationship between testis investment by male helpers and the number of offspring they sire

Female Pygmy Squid Cryptically Favour Small Males and Fast Copulation as Observed by Removal of Spermatangia

Females can express mate (or fertilisation) preferences after copulation. In the Japanese pygmy squid, Idiosepius paradoxus, in which males do not show any conspicuous pre-copulatory displays, the females remove the spermatangia attached to their bodies after copulation. In this study, we observed pre- and post-copulatory behaviours and analysed which variables associated with copulation were correlated with spermatangia removal. When females mated with larger males or copulation lasted longer female squid elongated their buccal mass after copulation and removed more spermatangia. We also investigated the effects of spermatangia removal on the retained spermatangia to predict whether cryptic female choice (CFC) influenced fertilisation success. Spermatangia removal by females had a stronger effect on the number of spermatangia retained than did the number of spermatangia ejaculated by males. These results suggest that spermatangia removal after copulation by buccal mass elongation works as a CFC in Japanese pygmy squid, and females cryptically favoured small males and fast copulation

The ART of mating : alternative reproductive tactics and mating success in a nest-guarding fish

Fish use different modalities to access mates for reproduction, often referred to as Alternative Reproductive Tactics (ARTs). ARTs are an example of coexisting phenotypes, which have to hold some degree of reproductive success to persist in a population. In the Mediterranean damselfish (Chromis chromis), territorial males colonise nests on rocky reefs, competing for females, while sneaker males attempt to parasitically spawn in those nests. Here we combine behavioural observations in the field with molecular analyses, using bi-parentally and maternally inherited markers, to investigate reproductive success patterns of the two observed male ARTs in terms of number of eggs sired and number of females contributing to each nest. Cuckoldry was observed in every nest sampled, with at least two and up to seven sneakers per nest; however, the nesting male always significantly fathered the large majority of the eggs (on average 49%) in each clutch. Each sneaker fathered around 7% of the clutch. The average number of females whose eggs were fertilised by nesting males was 6.76 (ranging 2-13), while each sneaker on average fertilised the eggs of 1.74 (range 1-8) females. Using this sibship reconstruction, we investigated some of the factors involved in the regulation of the dynamic equilibrium of reproductive success between the two ARTs showed by C. chromis males. Our results show that the sneakers’ reproductive success was positively linked to egg clutch size; the density of individuals in the nesting area negatively affected the size of egg clutches; the rate of defence behaviours performed by nesting males negatively influenced the number of females contributing to each nest

Spermatangium formation and sperm discharge in the Japanese pygmy squid Idiosepius paradoxus

In cephalopods, sperm discharge is an important event not only for sperm transfer but also influencing sperm storage capacity of attached spermatangia (everted spermatophores). To investigate sperm discharge from spermatangia and the condition of naturally attached spermatangia in Japanese pygmy squid (Idiosepius paradoxus) we (i) investigated the morphology of spermatophores and spermatangia, and the process of spermatophore evagination and sperm discharge from spermatangia obtained in vitro; (ii) observed spermatangia that were naturally attached to female squids at 6, 12, 18, 24 and 48. h after copulation to investigate alterations in naturally attached spermatangia with time. The spermatophore of I. paradoxus is slender and cylindrical and consists of a sperm mass, a cement body and an ejaculatory apparatus, which is similar to those of loliginid squids. The spermatangium is fishhook-shaped, its distal end being open and narrow. After the spermatangium is formed, the sperm mass gradually moves to the open end of the spermatangium, from where sperm are released. Sperm discharge is a rapid process immediately after the beginning of sperm release, but within 5. min changes to an intermittent release of sperm. Although the volume of residual spermatozoa differed among spermatangia that were naturally attached to a single individual, the probability that spermatangia would be empty increased with time. Most naturally attached spermatangia discharged almost all of their spermatozoa within 24. h after copulation, and no spermatangia were attached to females 48. h after copulation. These results suggest that sperm transfer from the spermatangium to the seminal receptacle must occur within 24. h, and that the spermatangium functions as a transient sperm storage organ in pygmy squids

Sperm transfer or spermatangia removal: postcopulatory behaviour of picking up spermatangium by female Japanese pygmy squid

In the Japanese pygmy squid Idiosepius paradoxus, females often pick up the spermatangium using their mouth (buccal mass) after copulation. To examine whether the female I. paradoxus directly transfers sperm into the seminal receptacle via this picking behaviour, or removes the spermatangium, we conducted detailed observations of picking behaviour in both virgin and copulated females and compared the sperm storage conditions in the seminal receptacle between females with and without spermatangia picking after copulation in virgin females. In all observations, elongation of the buccal mass occurred within 5 min after copulation. However, sperm volume in the seminal receptacle was not related to spermatangia picking. Observations using slow-motion video revealed that females removed the spermatangia by blowing or eating after picking. These results suggest that picking behaviour is used for sperm removal but not for sperm transfer. Moreover, the frequency of buccal mass elongation was higher in copulated females than in virgin females, consistent with the sequential mate choice theory whereby virgin females secure sperm for fertilisation, while previously copulated females are more selective about their mate. Female I. paradoxus may choose its mate cryptically through postcopulatory picking behaviour

Identification of larvae of two Gymnocanthus (Cottidae) species based on melanophore patterns

Gymnocanthus herzensteini and Gymnocanthus intermedius (Cottidae) larvae are common in northern Japan, but can be difficult to distinguish. In this study, morphological observations and mitochondrial DNA analyses were conducted to determine if melanophore patterns could be used to distinguish the two species. The morphological observations identified two groups with distinct melanophore patterns. Subsequent molecular analyses determined with high bootstrap values that the group with numerous body melanophores was G. intermedius, and the group with fewer melanophores was G. herzensteini. These results indicate that melanophore distribution patterns in larvae are useful for identifying G. intermedius and G. herzensteini

Karyological evidence of hybridogenesis in Greenlings (Teleostei: Hexagrammidae)

Two types of natural hybrids were discovered in populations of three Hexagrammos species (Teleostei: Hexagrammidae) distributed off the southern coast of Hokkaido in the North Pacific Ocean. Both hybrids reproduce by hybridogenesis, in which the maternal haploid genome is transmitted to offspring without recombination and the paternal haploid genome is eliminated during gametogenesis. While natural hybrids are unisexual and reproduce hemiclonally by backcrossing with the paternal species (BC-P), artificial F-1-hybrids between the pure species produce recombinant gametes. Thus, despite having the same genome composition, the natural hybrids and the F-1-hybrids are not genetically identical. Here, to clarify the differences between both hybrids, we examined the karyotypes of the three Hexagrammos species, their natural hybrids, the artificial F-1-hybrids, and several backcrosses. Artificial F-1-hybrids have karyotypes and chromosome numbers that are intermediate between those of the parental species. Conversely, the natural hybrids differed from F-1-hybrids by having several large metacentric chromosomes and microchromosomes. Since the entire maternal haploid genome is inherited by the natural hybrids, maternal backcrosses (BC-M) between natural hybrids and males of the maternal species (H. octogrammus; Hoc) have a hemiclonal Hoc genome with large chromosomes from the mother and a normal Hoc genome from the father. However, the large chromosomes disappear in offspring of BC-M, probably due to fissuring during gametogenesis. Similarly, microsatellite DNA analysis revealed that chromosomes of BC-M undergo recombination. These findings suggest that genetic factors associated with hemiclonal reproduction may be located on the large metacentric chromosomes of natural hybrids

A new cottid species, Icelus sekii (Perciformes: Cottoidei) from Hokkaido, Japan

A new cottid species, Icelus sekii, is described on the basis of six specimens collected from off Rausu and Urakawa, Hokkaido Island, Japan. This species is distinguished from its congeners by the following combination of characters: supraocular and parietal spines absent; nuchal spine obscure; uppermost preopercular spine unbranched; no scales between dorsal scale row and lateral-line scale row, and no scales below lateral-line scale row; supraocular, parietal, and nuchal cirri present; five dark brown saddles dorsolaterally; anal-fin rays 13; pectoral-fin rays 15; vertebrae 12 + 24~5 = 36~7. Icelus sekii can be mature at the smallest size among the species of Icelus. As a secondary sexual character, the male holotype has unique ensiform flaps on the distal tips of the first dorsal fin