The effect of alternative mating tactics on the fertilization success of a hermaphroditic seabass

In the simultaneously hermaphroditic marine fish, Serranus subligarius, male role individuals are known to pair spawn, group spawn and streak spawn. While the effects of these common mating tactics on mating success in the male role have been well studied, their consequences for the reproductive success of the individuals taking the female role have received little attention. To investigate those consequences, I observed mating behaviors and quantified fertilization success in natural and experimental settings during the summers of 2005-2008 at three sites with different local population densities. I observed focal individuals in 15-min increments and recorded the total number of spawns, number of streak spawns, size of participating spawners, and fertilization rate. The occurrence of small-sized individuals in the local population is associated with higher frequencies of streaking behavior; these small fish are most often first-year individuals reaching sexual maturity late in the spawning season (August/September). Spawns that included one or more streak spawners had a significantly lower average fertilization rate (89?%) than pair spawns without a streak spawner (97?%). This pattern was confirmed with a field manipulation experiment in which spawning events that included streakers again showed lower fertilization rates (93?%) than spawning events that did not include streakers (98?%). These lower fertilization rates occurred despite the fact that spawns that included multiple males produced, on average, 20?% more sperm than produced in spawns with only a single male. These results indicate that females incur a significant fitness cost when streakers invade a spawning event, a cost not attributable to sperm limitation or any direct effects on the female.     

Group III muscle afferents evoke reflex depressor responses to repetitive muscle contractions in rabbits

Repetitive-twitch contraction of the hindlimb muscles in anesthetized rabbits consistently evokes a reflex depressor response, whereas this type of contraction in anesthetized cats evokes a reflex pressor response in about one-half of the preparations tested. Rapidly conducting group III fibers appear to comprise the afferent arm of the reflex arc, evoking the depressor response to twitch contraction in rabbits because electrical stimulation of their axons reflexly decreases arterial pressure. In contrast, electrical stimulation of the axons of slowly conducting group III and group IV afferents reflexly increases arterial pressure in rabbits. In the present study, we examined the discharge properties of group III and IV muscle afferents and found that the former (i.e., 13 of 20), but not the latter (i.e., 0 of 10), were stimulated by 5 min of repetitive-twitch contraction (1 Hz) of the rabbit triceps surae muscles. Moreover, most of the group III afferents responding to contraction appeared to be mechanically sensitive, discharging in synchrony with the muscle twitch. On average, rapidly conducting group III afferents responded for the 5-min duration of 1-Hz repetitive-twitch contraction, whereas slowly conducting group III afferents responded only for the first 2 min of contraction. We conclude that rapidly conducting group III afferents, which are mechanically sensitive, are primarily responsible for evoking the reflex depressor response to repetitive-twitch contractions in anesthetized rabbits.     

Courtship and Spawning Behavior in the California Sheephead, Semicossyphus Pulcher (Pisces: Labridae)

We recorded the courtship and spawning behavior of a protogynous fish, the California sheephead, Semicossyphus pulcher, throughout their spawning season at Bird Rock, Santa Catalina Island, California. We made additional observations at the Monterey Bay Aquarium and confirmed the details of behavior seen in the field. Large males held spawning territories in which females congregated approximately 1 h before sunset. Courtship commenced shortly before sunset and involved the male approaching each female, making lateral contact and leading her in a circular pattern. Smaller males attempted to court females within the territories, prompting large males to abort spawns and engage in chasing behavior with small males. Females visited several territorial males throughout the day, indicating that they are not part of a strict harem. Both field and aquarium observations confirm that the mating system can be successfully predicted from the size advantage model. Current regulations on the sheephead fishery, which allow for the removal of large, rare males, could have significant effects on the social structure, reproductive output, and mating processes of local populations. Moreover, understanding the mating system of the California sheephead illustrates the need for creating management strategies that better complement the unique life histories of marine fishes with alternative reproductive strategies.     

Responses of group III and IV muscle afferents to dynamic exercise

Adreani, Christine M., Janeen M. Hill, and Marc P. Kaufman.Responses of group III and IV muscle afferents to dynamic exercise. J. Appl. Physiol. 82(6):1811-1817, 1997.Tetanic contraction of hindlimb skeletal muscle,induced by electrical stimulation of either ventral roots or peripheralnerves, is well known to activate group III and IV afferents.Nevertheless, the effect of dynamic exercise on the discharge of thesethin fiber afferents is unknown. To shed some light on this question,we recorded in decerebrate cats the discharge of 24 group III and 10 group IV afferents while the mesencephalic locomotor region (MLR) wasstimulated electrically. Each of the 34 afferents had their receptivefields in the triceps surae muscles. Stimulation of the MLR for 1 min caused the triceps surae muscles to contract rhythmically, an effectinduced by an -motoneuron discharge pattern and recruitment orderalmost identical to that occurring during dynamic exercise. Eighteen ofthe 24 group III and 8 of the 10 group IV muscle afferents werestimulated by MLR stimulation. The oxygen consumption of thedynamically exercising triceps surae muscles was increased by 2.5-foldover their resting levels. We conclude that low levels of dynamicexercise stimulate group III and IV muscle afferents.

     

Effect of arterial occlusion on responses of group III and IV afferents to dynamic exercise

Our laboratory has shownpreviously that a low level of dynamic exercise induced by electricalstimulation of the mesencephalic locomotor region (MLR) stimulatedgroup III and IV muscle afferents in decerebrate unanesthetized cats(C. M. Adreani, J. M. Hill, and M. P. Kaufman. J. Appl. Physiol. 83: 1811-1817, 1997). In thepresent study, we have extended these findings by examining the effectof occluding the arterial supply to the dynamically exercising muscleson the afferents' responses to MLR stimulation. In decerebrate cats,we found that arterial occlusion increased the responsiveness to a lowlevel of dynamic exercise in 44% of the group III and 47% of thegroup IV afferents tested. Occlusion, compared with the freely perfusedstate, did not increase the concentrations of either hydrogen ion orlactate ion in the venous effluent from the exercising muscles. Weconclude that arterial occlusion caused some unspecified substance toaccumulate in the working muscles to increase the sensitivity of equalpercentages of group III and IV afferents to dynamic exercise.

     

Cohort cultures of Psammoryctides barbatus (Grube) and Spirosperma ferox Eisen: a tool for a better understanding of demographic strategies in Tubificidae

Laboratory research on the tubificids Psammoryctides barbatus and Spirosperma ferox was done. Embryonic development time, growth, time required to attain the first cocoon laying and egg production were estimated at different temperatures and population densities. The results allow us to demonstrate some intrinsic density regulation mechanisms in the profundal tubificid communities and substantiate the hypothesis that the succession from oligotrophic to eutrophic species in the profundal of lakes undergoing eutrophication is mainly based on their biotic characteristics.