No abstract

The mating behavior of captive Loligo bleekeri and the paternity of the resulting progeny were examined based on behavioral observations and genetic analyses. In this species, there are 3 mating behaviors (male-parallel, head-to-head, and extra-pair), and 2 sperm storage sites in females (seminal receptacle and the opening of the oviduct), which suggest that sperm competition occurs. All 3 mating behaviors were observed, and females mated often with different males, resulting in multiple paternity within 3 of the 4 broods examined. In each brood, the male to mate last and frequently before the female spawned fertilized the most eggs (87 to 100%). A sneaker male that mated by extra-pair copulation sired 8.5% of the eggs in a brood. Some eggs were fertilized by sperm received before the start of the study, indicating that sperm can be stored for at least several days before a spawning. In the broods with multiple paternity, the paternity patterns differed among egg capsules. Male competition was more intense between similar-sized males than between differentsized males, but body size did not affect the copulative success in the male-parallel position. We found multiple mating and multiple paternity in L. bleekeri. Paternity rates differed depending on the complex of factors, mating position, timing, frequency and duration. Alternative reproductive behaviors would change these factors and lead to different paternity rates.KEY WORDS: Multiple paternity · Reproductive strategy · Squid · Loligo · Microsatellite · Sperm competition Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 298: [219][220][221][222][223][224][225][226][227][228] 2005 just before she spawns . These consort males guard females before and after copulation and while the females spawn, but sometimes large intruders replace the consort males and copulate with the females . Furthermore, extra-pair copulations (EPCs) also occur, in which a small 'sneaker male' copulates with a female that is paired with another male by attaching spermatophores near the female's mouth (Hanlon 1996. The spermatozoa are stored until they are released at spawning, so loliginid females can use spermatozoa from several males when they spawn.When squids spawn, eggs are extruded from the oviduct and pass through the funnel to a position near the mouth. The eggs can be fertilized either as they leave the oviduct, by spermatozoa placed in the mantle cavity during a male-parallel mating, or near the mouth, by spermatozoa stored in the seminal receptacle after a head-to-head mating or EPC. This difference in the fertilization mechanism will presumably affect the reproductive success of each copulative behavior and play a role in sexual selection (Birkhead & Møller 1998).If the reproductive success of each copulative behavior differs, males will compete to mate in the favorable position. Agonistic behavior between males has been shown to escalate through several phases, from visual signaling to physical contact (DiMarco & Ha...

The Oyashio shelf region and the seasonally ice-covered areas north of Hokkaido are highly productive, supporting a wide range of species including marine mammals, seabirds and commercially important species in the western subarctic Pacific. The fishes include gadids, such as walleye pollock and Pacific cod, and subarctic migratory pelagic fishes such as chum salmon and pink salmon. It is also an important summer feeding ground for subtropical migrants such as the Japanese sardine, Japanese anchovy, Pacific saury, mackerels, Japanese common squid, whales and seabirds. In recent decades, some components of the Oyashio ecosystem (i.e., phytoplankton, mesozooplankton, gadid fish, and subtropical migrants) have shown changes in species abundance or distribution that are correlated with environmental changes such as the 1976/77 and 1988/89 regime shifts. The First Oyashio Intrusion moved northward from the mid 1960s until the late 1970s when it moved southward until the 1980s, after which it returned to the north again after the mid 1990s. The sea surface temperature in spring decreased after the late 1970s, increased after the late 1980s, and remained high during the 1990s. The extent of ice cover in the Sea of Okhostk also decreased during the latest warming in the 1980-90s but has increased again since the late 1990s. These and other kinds of variability are described in this overview of the status of the Oyashio ecosystem and the surrounding region.

Male dimorphism has been thought to correlate with alternative reproductive behaviors. Alternative reproductive behaviors promote asymmetry in sperm competition, and the differences in fertilization success could promote adaptations in ejaculate characteristics in relation to each reproductive behavior. Using allometric analysis, we show that ejaculate dimorphism clearly exists in males of the squid Loligo bleekeri, a cephalopod species with body size-related alternative mating behaviors. A morphological switch point was detected for internal characters: larger individuals produced discontinuously longer spermatophores than did smaller individuals, although no switch point was detected for external characteristics (fin length, fin width, head width, mantle width, tentacle length and hectocotylus length) except for bimodal body size. This clear internal switch point could be an adaptation to the characteristic alternative mating behaviors of loliginid squid, in which males use different mating tactics to pass spermatophores to different sperm storage sites in and on the females. Our results indicated that alternative reproductive behaviors can result in morphological adjustment in internal characteristics. KEY WORDS: Male dimorphism · Sperm competition · Alternative reproductive behavior · Squid · Loligo bleekeri Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 345: [141][142][143][144][145][146] 2007 squid, however, have 2 distinct sperm storage sites (the seminal receptacle near the mouth and the opening of the oviduct within the mantle cavity), which corresponds to alternative mating behaviors (Hanlon & Messenger 1996). Loliginid squids form dense spawning aggregations on coastal spawning grounds, and males pair temporarily with females in order to mate (Hanlon & Messenger 1996). These spawning aggregations usually tend to have more males than females and the mating behaviors that males use correlate with their body size: large males pair with females and copulate in the male parallel position by attaching spermatophores to the female's oviduct in the mantle cavity, and small sneaker males mate in the head-to-head position by attaching spermatophores near the mouth of females that have already paired with other males (Hanlon et al. 1997(Hanlon et al. , 2002. Sneaker males fertilize fewer eggs than paired males do (Iwata et al. 2005). This suggests that sperm stored near the oviduct have an advantage, perhaps because they are stored closer to the eggs being spawned than are sperm stored in the seminal receptacle near the mouth. These size-dependent alternative mating behaviors and the differences in fertilization success could promote strategic ejaculation in males specializing on different sperm-passing sites. Furthermore, loliginid males pass sperm as spermatophores, enclosing the spermatozoa within a hard shell, and males store several hundred spermatophores when they mature. Therefore, the ejaculate characteristics associated with a male's status c...

The population genetic structure and level of gene flow of Nibea albiflora from the Yellow Sea and the East China Sea were examined with a 479-bp segment of a mtDNA control region. In total, 65 samples were collected from three locations and 37 haplotypes were obtained. Mean haplotype diversity and nucleotide diversity for the three populations ranged from 0.9130 Ϯ 0.0308 (Zhoushan) to 0.9926 Ϯ 0.0230 (Xiamen), and from 0.0073 Ϯ 0.0043 (Qingdao) to 0.0099 Ϯ 0.0057 (Xiamen). Analysis of molecular variance and pairwise FST revealed little genetic structure between the Yellow Sea and the East China Sea in N. albiflora. But based on the exact test of differentiation, the null hypothesis that N. albiflora within the Yellow Sea and the East China Sea constitutes a panmictic mtDNA gene pool was rejected. This might be caused by the broad spawning areas but not by the Yangtze River outflow. Mismatch distribution revealed that N. albiflora has undergone population expansion, possibly before the last 85 000-170 000 years. The existence of high gene flow between stocks in the studied area was supported by our results. Annual migrations, larval drift in the ocean currents, and recent range expansion could be the reasons for little genetic structure in the studied area.