Filial cannibalism in a paternal mouthbrooding fish in relation to mate availability

Abstract. Cannibalism of the entire brood by mouthbrooding males was observed in the cardinal fish, Apogon doederleini, in warm temperate waters of southern Japan. This filial cannibalism always occurred within a day of spawning. Males preferentially ate broods produced by females smaller than themselves and by non-resident females, and always changed mates after cannibalism. Cannibalistic males re-mated more quickly than males whose broods were experimentally removed. These results indicate that cannibalistic males take advantage of multiple mate availability, by eating the first brood and rearing the second. It is suggested that filial cannibalism in this fish is associated with mating strategies of females that can shorten inter-spawning intervals by changing mates. 1996 The Association for the Study of Animal Behaviou

Sexual selection of male parental care in giant water bugs

Paternal care can be maintained under sexual selection, if it helps in attracting more mates. We tested the hypothesis in two giant water bug species, Appasus major and Appasus japonicus, that male parental care is sexually selected through female preference for caring males. Females were given an opportunity to choose between two males. In the first test of female mate choice, one male carried eggs on its back, while the other did not. The egg status was switched between these two males in the second test. The experiment revealed that females of both species preferred caring males (i.e. egg-bearing) to non-caring males. Nonetheless, the female mate preference for egg-bearing males was stronger in A. major than in A. japonicus. Our results suggest that sexual selection plays an important role in maintaining elaborate paternal care in giant water bugs, but the importance of egg-bearing by males in female mate choice varies among species

Seasonal and site-specific variability in terrigenous particulate organic carbon concentration in near-shore waters of Lake Biwa, Japan

Identifying sources of particulate organic matter (POM) is important for clarifying fundamental mechanisms by which lake food webs are sustained. We determined carbon and nitrogen stable isotope ratios of POM in near-shore waters of Lake Biwa, a large, meso-eutrophic lake in Japan, to estimate relative contributions of terrigenous particulate organic carbon (T-POC), plankton-derived POC (P-POC) and epilithon-derived POC (E-POC) to POC in near-shore waters. Samples were collected during different months (November, February, May and July) at 29 sites located near the mouth of tributary rivers with different discharge and catchment land use. The data revealed that POC mainly consisted of P-POC and T-POC, with relative contributions varying widely over season and among locations. E-POC generally contributed little to the near-shore POC. Path analyses revealed that the concentration of riverine POC whose isotopic signatures were similar to those of rice straws increased with a larger %paddy field area in the catchment of tributary rivers, which subsequently enhanced T-POC inputs to near-shore waters through riverine transportation. Furthermore, our results suggested that T-POC contribution was influenced, with a time lag, by wave-driven turbulence and shore topography, which appear to affect sedimentation and resuspension of T-POC

Is the Relationship between Body Size and Trophic Niche Position Time-Invariant in a Predatory Fish? First Stable Isotope Evidence

Characterizing relationships between individual body size and trophic niche position is essential for understanding how population and food-web dynamics are mediated by size-dependent trophic interactions. However, whether (and how) intraspecific size-trophic relationships (i.e., trophic ontogeny pattern at the population level) vary with time remains poorly understood. Using archival specimens of a freshwater predatory fish Gymnogobius isaza (Tanaka 1916) from Lake Biwa, Japan, we assembled a long-term (>40 years) time-series of the size-dependence of trophic niche position by examining nitrogen stable isotope ratios (δ15N) of the fish specimens. The size-dependence of trophic niche position was defined as the slope of the relationship between δ15N and log body size. Our analyses showed that the slope was significantly positive in about 60% of years and null in other years, changing through time. This is the first quantitative (i.e., stable isotope) evidence of long-term variability in the size-trophic relationship in a predatory fish. This finding had implications for the fish trophic dynamics, despite that about 60% of the yearly values were not statistically different from the long-term average. We proposed hypotheses for the underlying mechanism of the time-varying size-trophic relationship

Mixing Regimes in a Cluster of Seven Maar Lakes in Tropical Monsoon Asia

The 7 maar lakes of San Pablo are a cluster of small volcanic lakes on Luzon Island; Philippines. These lakes; which are heavily utilized for aquaculture and ecotourism; usually experience fish kills that coincide with the northeast monsoon (NEM). This study explores limnophysical processes; particularly mixing regimes; in the lakes in relation to prevailing monsoons. We monitored monthly vertical and seasonal profiles of water temperature; salinity; conductivity; and dissolved oxygen from October 2016 to December 2018. Three types of mixing regimes were observed among the lakes; which have similar surface areas but different depths: polymixis in the shallowest; warm monomixis in lakes with intermediate depth; and meromixis in the deepest. A boundary between monomixis and meromixis was identified between 36 and 62 m depth. Monthly monitoring showed seasonal mixing occurred exclusively during the NEM (Nov–Apr). We also incorporated meteorological data into the model and performed multiple regression analysis for each lake to determine the best predictor: lake stability; as indicated by the Schmidt stability (ST). A between-lake comparison showed lake stability was strongly correlated with both air temperature and wind speed; suggesting these 2 meteorological variables are involved in establishing thermal stratification in the lakes during the southwest monsoon. This study provides insights for adaptive lake management and projections of climate impacts on these understudied tropical lake ecosystems in Southeast Asia

Development of Nine Markers and Characterization of the Microsatellite Loci in the Endangered Gymnogobius isaza (Gobiidae)

Gymnogobius isaza is a freshwater goby endemic to Lake Biwa, Japan. They experienced a drastic demographic bottleneck in the 1950s and 1980s and slightly recovered thereafter, but the population size is still very small. To reveal dynamics of genetic diversity of G. isaza, we developed nine microsatellite markers based on the sequence data of a related goby Chaenogobius annularis. Nine SSR (Simple Sequence Repeats) markers were successfully amplified for raw and formalin-fixed fish samples. The number of alleles and expected heterozygosities ranged from one to 10 and from 0.06 to 0.84, respectively, for the current samples, while one to 12 and 0.09 to 0.83 for historical samples. The markers described here will be useful for investigating the genetic diversity and gene flow and for conservation of G. isaza

Nature and Happiness Levels: New SWB Domains for Rivers, a Lake, and Forests

By using a questionnaire survey, we measured nature-related happiness levels, which include specific domains that differ from the overall subjective well-being (SWB) in a Japanese watershed. We regarded nature-related happiness levels, specifically related to rivers, a lake, or forests, as meaningful indices because many people living separated from nature may be unaware of their relationship with nature. We found that nature-related happiness levels had convergent validity and distinct correlation patterns with the explanatory variables, and these patterns were different from those of the overall SWB. These findings support the case of measuring nature-related happiness levels and overall SWB. Nature-related happiness levels were positively correlated with leisure activities and contact with living things. The abundance of rivers in a district is negatively associated with river-related happiness. We speculated that this was due to unidentified disservices associated with the rivers. Lake-related happiness has stronger correlations with relaxation benefits than symbolism, local food culture, art/culture, or water sources. Considering these findings, policymakers should formulate policies based on nature-related happiness levels. Because nature-related happiness levels are not correlated with income level, such policies may contribute to residents’ well-being in an egalitarian manner

Utility of Nd isotope ratio as a tracer of marine animals : regional variation in coastal seas and causal factors

Isotopic compositions of animal tissue are an intrinsic marker commonly used to trace animal origins and migrations; however, few isotopes are effective for this purpose in marine environments, especially on a local scale. The isotope ratio of the lanthanoid element neodymium (Nd) is a promising tracer for coastal animal migrations. Neodymium derives from the same geologic materials as strontium, well known as an isotopic tracer (87Sr/86Sr) for terrestrial and anadromous animals. The advantage of the Nd isotope ratio (143Nd/144Nd, expressed as εNd) is that it varies greatly in the ocean according to the geology of the neighboring continents, whereas oceanic 87Sr/86Sr is highly uniform. This study explored the utility of the Nd isotope ratio as a marine tracer by investigating the variation of εNd preserved in tissues of coastal species, and the causes of that variation, in a region of northeastern Japan where the bedrock geology is highly variable. We measured εNd and 87Sr/86Sr in seawater, river water, and soft tissues of sedentary suspension feeders: the mussels Mytilus galloprovincialis and Mytilus coruscus and the oyster Crassostrea gigas. We also measured concentrations of three lanthanoids (La, Ce, and Pr) in shellfish bodies to determine whether the Nd in shellfish tissue was derived from solution in seawater or from suspended particulates. The εNd values in shellfish tissue varied regionally (−6 to +1), matching the ambient seawater, whereas all 87Sr/86Sr values were homogeneous and typical of seawater (0.7091–0.7092). The seawater εNd values were in turn correlated with those in the adjacent rivers, linking shellfish εNd to the geology of river catchments. The depletion of Ce compared to La and Pr (negative Ce anomaly) suggested that the Nd in shellfish was derived from the dissolved phase in seawater. Our results indicate that the distinct Nd isotope ratio derived from local geology is imprinted, through seawater, on the soft tissues of shellfish. This result underscores the potential of εNd as a tracer of coastal marine animals