Past and present distribution, densities and movements of blue whales Balaenoptera musculus in the Southern Hemisphere and northern Indian Ocean

• 1 Blue whale locations in the Southern Hemisphere and northern Indian Ocean were obtained from catches (303 239), sightings (4383 records of ≥8058 whales), strandings (103), Discovery marks (2191) and recoveries (95), and acoustic recordings.
• 2 Sighting surveys included 7 480 450 km of effort plus 14 676 days with unmeasured effort. Groups usually consisted of solitary whales (65.2%) or pairs (24.6%); larger feeding aggregations of unassociated individuals were only rarely observed. Sighting rates (groups per 1000 km from many platform types) varied by four orders of magnitude and were lowest in the waters of Brazil, South Africa, the eastern tropical Pacific, Antarctica and South Georgia; higher in the Subantarctic and Peru; and highest around Indonesia, Sri Lanka, Chile, southern Australia and south of Madagascar.
• 3 Blue whales avoid the oligotrophic central gyres of the Indian, Pacific and Atlantic Oceans, but are more common where phytoplankton densities are high, and where there are dynamic oceanographic processes like upwelling and frontal meandering.
• 4 Compared with historical catches, the Antarctic (‘true’) subspecies is exceedingly rare and usually concentrated closer to the summer pack ice. In summer they are found throughout the Antarctic; in winter they migrate to southern Africa (although recent sightings there are rare) and to other northerly locations (based on acoustics), although some overwinter in the Antarctic.
• 5 Pygmy blue whales are found around the Indian Ocean and from southern Australia to New Zealand. At least four groupings are evident: northern Indian Ocean, from Madagascar to the Subantarctic, Indonesia to western and southern Australia, and from New Zealand northwards to the equator. Sighting rates are typically much higher than for Antarctic blue whales.
• 6 South‐east Pacific blue whales have a discrete distribution and high sighting rates compared with the Antarctic. Further work is needed to clarify their subspecific status given their distinctive genetics, acoustics and length frequencies.
• 7 Antarctic blue whales numbered 1700 (95% Bayesian interval 860–2900) in 1996 (less than 1% of original levels), but are increasing at 7.3% per annum (95% Bayesian interval 1.4–11.6%). The status of other populations in the Southern Hemisphere and northern Indian Ocean is unknown because few abundance estimates are available, but higher recent sighting rates suggest that they are less depleted than Antarctic blue whales.

     

Host-dependent differences in prey acquisition between populations of a kleptoparasitic spider Argyrodes kumadai (Araneae: Theridiidae)

Abstract.  1. A kleptoparasitic spider, Argyrodes kumadai , is known to use phylogenetically unrelated host species in different regions – Cyrtophora moluccensis (Araneidae) in south-west Japan and Agelena silvatica (Agelenidae) in north-east Japan. The work reported here examined whether differences in host characters affect prey acquisition of A. kumadai .
2. Field surveys showed that prey-biomass capture rate of Argyrodes was significantly higher in populations parasitising Cyrtophora than in populations parasitising Agelena . Although Argyrodes appeared to catch fewer prey within Cyrtophora webs, they were able to feed upon substantially larger prey.
3. Differences in prey-biomass capture rate were found to reflect differences in host traits rather than regional differences in potential prey availability. Individuals in populations parasitising Cyrtophora were observed to acquire prey via a number of foraging tactics that included stealing wrapped food bundles, feeding upon prey remains and, in the case of large prey items, feeding together with the host. In contrast, individuals in populations parasitising Agelena were only ever observed to feed upon small prey items ignored by its host.
4. This variability in prey acquisition between kleptoparasite populations reflected different opportunities for feeding within their respective host webs – opportunities that were primarily determined by the foraging behaviour of the host. One key trait associated with host foraging behaviour was host-web structure, namely the presence/absence of a retreat.     

Origins of Laboratory Mice Deduced from Restriction Patterns of Mitochondrial DNA

To determine the origins of laboratory mice, the restriction patterns of mitochondrial DNAs (mtDNAs) from various strains were compared with those of relevant subspecies and/or races of mus musculus . In most strains and substrains of laboratory mice examined (50/55), the cleavage patterns were identical to those of the European subspecies M. m. domesticus . Those that varied include two sublines of NZB, the strain NZC, and the Japanese strain RR. The NZB and NZC patterns were identical to that of the European subspecies M. m. brevirostris , which itself has restriction patterns similar to M. m. domesticus . On the other hand, the RR pattern was identical to M. m. molossinus -like mice trapped in Western China and slightly different from Japanese M. m. molossinus . These findings suggest that the strains NZB and NZC stemmed from a European founder stock which differed from the ancestral stocks of other laboratory strains and that the ancestral mice of the RR strain had been transported from China to Japan. Therefore, most laboratory strains of mice are derived from the European subspecies M. m. domesticus while M. m. brevirostris and M. m. molossinus have made minor contributions. M. m. musculus does not appear to have made any contribution.     

Presence of the water lily,Trapa natans L., increases fitness of the water strider,Gerris nepalensis

Abstract Exposure of the waterstrider, Gerris nepalensis, to leaves of the water lily, Trapa natans, during either the larval or adult stage increases the proportion of reproductive females (60.0%) and increases the number of eggs laid by G. nepalensis (25.1 ± 8.1) compared with leaves of another floating plant, Hydrocharis dubia (20.2%, 6.7 ± 17.8), and mimic leaves made of polystyrene (24.2%, 20.0 ± 16.9). The larval period at 25 °C is significantly shorter when larvae are reared together with water lily leaves than when reared with mimic leaves made of thin styrene. A significantly higher percentage (76.4 ± 39.9) of eggs laid by females that are reared with lily leaves in larval and adult stages develop successfully to the first instar compared with those reared with ‘mimic‐leaves’ (% hatched‐out successfully: 53.9 ± 39.3). The effect of T. natans on G. nepalensis demonstrated in the present study is to increase the number of G. nepalensis in the habitat and likely increase foraging pressure on the lily leaf beetle, Galerucella nipponensis. Possible mechanisms of this relationship between T. natans and G. nepalensis are discussed.     

Mussel responses to flood pulse frequency: the importance of local habitat

1. Understanding mechanisms behind the distribution of organisms along a gradient of hydrological connectivity is crucial for sustainable management of river–floodplain systems. We tested the hypothesis that frequency of flood pulses exerts a direct influence on the distribution of freshwater mussels (Unionoida) by creating a local environment that limits their fitness. 2. Multiscale habitat analyses combined with transplant‐rearing experiments were carried out with a focus on abundance, presence/absence, survival rates and growth rates of mussels. Sixty‐nine floodplain waterbodies (FWBs) were surveyed within a 15‐km lowland segment of the Kiso River in Japan. 3. The abundance of mussels significantly increased with increased frequency of inundation associated with flood pulses at the among‐FWB scale, while the probability of occurrence of mussels was negatively predicted by the amount of benthic organic matter at the within‐FWB scale. 4. Field‐rearing experiments showed that survival rates were low and growth rates nearly zero in infrequently inundated FWBs (these FWBs had no naturally occurring resident mussels). In such FWBs, hypoxia (DO < 2 mg L^?1) was frequently observed near the bottom when temperature was optimal for mussel growth (>15 °C). 5. These findings demonstrated that flood pulse frequency was the most important factor in determining mussel distribution in FWBs because it directly limits mussels’ fitness by mediating local environmental factors, possibly dissolved oxygen (DO) levels. Successful restoration efforts for mussel habitat conservation should focus on processes that lead to improved local conditions.     

Impact of exotic fish removal on native communities in farm ponds

Introduced largemouth bass (Micropterus salmoides spp.) and bluegill (Lepomis macrochirus spp.) are thought to threaten native aquatic organisms worldwide and hence their eradication has recently begun in Japan. Our previous studies suggested that the removal of largemouth bass increases native fish, shrimp, dragonflies, and exotic crayfish, but decreases macrophytes. To test this prediction, we removed the exotic fishes by draining farm ponds and compared the numbers of these organisms before and after the drain, as well as between drained and undrained ponds. The number of dragonfly Pseudothemis zonata, crayfish, shrimp, and goby increased rapidly after the drain, but the coverage of macrophyte declined. The reduction in macrophyte is assumed to be caused by increased herbivory by crayfish. The number of exuviae of damselfly Cercion calamorum and the total number of species of odonate also decreased after the drain. These decreases can be due to the reduction of macrophyte because reduced odonate species are known to use macrophytes as oviposition sites. Therefore, the removal of largemouth bass has a potential to cause negative effects on some native organisms. We propose that reduction of exotic crayfish should be considered when eradicating the exotic fishes.