The costs of intersexuality: a crustacean perspective

Increasing concerns over rising intersexuality in the animal kingdom and the ability of certain chemicals to disrupt the endocrine system have demanded a better understanding of the costs associated with such conditions. Whilst intersexuality appears relatively widespread throughout gonochoristic crustaceans, i.e. those crustacean species with two separate sexes, the fitness costs have rarely been reported. Through comparable investigation of normal and intersex specimens of the highly abundant marine/estuarine amphipod Echinogammarus marinus (Leach) these fitness costs were determined. Measurements taken to assess fitness costs included fecundity, fertility and embryonic development, maturation period, and any morphological deformities that might result in reduced pairing success. Results from this study suggest that intersex E. marinus suffer from reduced fecundity and fertility, and mature at a larger size than normal specimens. These fitness costs can also, to a certain extent, be related to the degree of intersexuality. It is suggested that the increased size and morphological abnormalities observed in intersexes may result in reduced pairing success. Investigations into intersex organisms, i.e. those organisms with known dysfunctional endocrine systems, and the costs associated with such conditions, should aid researchers in assessing effects at the population and community level.Communicated by J.P. Thorpe, Port Erin     

Respiration rates of<Emphasis Type="Italic"> Beroe ovata</Emphasis> in the Black Sea

Metabolic rates of the ctenophore Beroe ovata within the length range from 0.4 mm (newly hatched larvae) to 60 mm were investigated. At 20° the respiration rates (Q, µg O₂ ind.^–1 h^–1) of individuals with wet weights (W, mg) less than or greater than 100 mg changed according to the equations Q=0.093W^0.62 and Q=0.016W^0.99, respectively. The weight-specific respiration rate of the juvenile ctenophores with wet body weights of 0.021–100 mg diminished approximately 20-fold (from 0.35 to 0.017 µg O₂ mg^–1 h^–1, respectively), but did not change within the range from 100 to 30,000 mg. The difference in the slope of the regression lines seems to be attributable to the ontogenetic changes in B. ovata metabolism. For the tested temperature range of 10–28°, the mean Q₁₀ coefficient was equal to 2.17±0.5. The basal metabolism of B. ovata narcotised by chloral hydrate was 4.5±0.9 times lower than total metabolism. Such a metabolic range is considered to be characteristic of aquatic invertebrates with high levels of locomotory activity.Communicated by O. Kinne, Oldendorf/Luhe     

Route of egg yolk protein uptake in the oocytes of kuruma prawn,Penaeus japonicus

The route of egg yolk protein uptake into the oocytes of kuruma prawn, Penaeus japonicus, was studied using immunohistochemical and electron microscopical methods. Although a significant immunofluorescence with anti-vitellin-immunoglobulin was observed in the enlarged follicle cells surrounding oil globule stage oocytes of the early vitellogenic ovary, no fluorescence was detected in shrunken follicle cells surrounding oocytes in the yolk granule stage. Electron microscopically, yolk granule stage oocytes have an irregular surface with numerous well-developed microvilli. In contrast, the surface of follicle cells is relatively smooth. The irregular surface of yolk granule stage oocytes was covered with a layer of electron dense material. Similar dense material was found in the spaces between the neighboring follicle cells on the yolk granule stage oocytes. The outer surface of the follicle cells on yolk granule stage oocytes was covered by dense materials which were similar to those found on the irregular surface of oocytes. Micropinocytotic vesicles containing dense material were found in the ooplasm near the irregular surface with numerous well-developed microvilli. Dense material was concentrated in the peripheral part of the small forming yolk bodies of yolk granule stage oocytes. This suggests that the electron dense material, probably egg yolk protein, transferred to the surface of yolk granule stage oocytes from the spaces between the neighboring follicle cells may be incorporated into the ooplasm by pinocytosis through the microvilli and subsequently aggregate to form yolk bodies.     

Interception and dispersal of artificial food falls by scavenging fishes in the abyssal Northeast Atlantic: early-season observations prior to annual deposition of phytodetritus

The hypothesis that the behaviour of deep-sea scavenging fishes is influenced by seasonal input of organic matter from the ocean surface was investigated by observing responses to baits placed on the sea floor at 4800 m depth in the NE Atlantic (48°50′N; 16°30′W) during spring (April 1994). Data from the present study are compared with those from previous studies of the same location made in summer 1989. The first fishes to arrive at baits were the grenadier Coryphaenoides (Nematonurus) armatus and the eel Histiobranchus bathybius, after delays of 28 and 29 min, respectively; these results are not significantly different from those of summer 1989. Similarly, other indices of activity (staying time and swimming speed) showed no evidence of differences between years/seasons. However, the rate of radial dispersal of bait (0.009 m s⁻¹) by C. (N.) armatus was much slower than in all previous studies. A change in the size distribution of C. (N.) armatus to smaller individuals in spring 1994 was also evident. It is suggested that the fish on the abyssal plain may not comprise a steady-state population and that major episodic or seasonal migrations may occur. Received: 18 October 1996 / Accepted: 20 December 1996     

The effect of lead bioaccumulation on haem biosynthetic enzymes in fish

The bioaccumulations of lead in the liver and hepatic microsomes of fish after 1, 3, 7, 14, 28, and 45 days exposure were studied. In addition, the relationship between the bioaccumulated lead in both hepatic microsomes and the liver and their haem biosynthetic enzymes were studied. Lead toxicity was shown to result in a depression of the microsomal mixed function oxidase system, as assessed by a decrease in hepatic microsomal cytochrome P-450 and b5 content and by a decrease in the activity of the enzymes aniline hydroxylase and aminopyrine demethylase. Lead had a more marked effect on cytochrome P-450 than b5. The activity of the rate-limiting enzyme of haem biosynthesis, delta-aminolevulinic acid synthase, was inversely correlated with the microsomal cytochrome P-450 content. The activity of the heam biosynthetic enzymes delta-aminolevulinic acid dehydratase, coproporphyrinogen oxidase and ferrochelatase were decreased by increasing lead pretreatment. The activity of the haem catabolic enzyme, haem oxygenase, was increased by concentration and length of time to lead exposure.     

Fish in larger shoals find food faster

Summary Experiments on shoaling cyprinids hunting for food on patches in tanks demonstrate and advantage of foraging in a group. Individual goldfish (Carassius auratus) and minnows (Phoxinus phoxinus) in a shoal of conspecifics located food more rapidly as shoal size increased from 2 to 20. although shoaling minnows form polarised schools more readily than goldfish, which rarely do so, both species benefited from the trend of speedier food location with increasing group size.     

Advanced age for sexual maturity in the ocean quahog Arctica islandica (Mollusca: Bivalvia)

A study of gonadal state in 39 small specimens of Arctica islandica Linné collected in April 1976 from the Middle Atlantic shelf of North America suggests that sexual maturity is reached at a later age than has been reported for other shelf bivalves. Eight of the specimens had gonads in the undifferentiated state. On the basis of annual internal growth banding in the shells of these immature specimens, age ranged between 4 and 14 years. Average age was 9.38 years (standard deviation, s,= 3.54). Shell length ranged from 24 to 47 mm (average 38.85 mm, s=9.25). Differentiated gonads were found in specimens as young as 6 years. Age of maturity shows a wide range and may be dependent upon growth rate and locality.     

Bacterial populations as components of oceanic ecosystems

The production of bacterioplankton in tropical waters is shown to be a major food source for filter feeders. Since this production greatly exceeds autotrophic production by phytoplankton, the external energy source is believed to be soluble organic material transported from temperate latitudes. In the latter environment this material is produced as part of excessive autotrophic production, but its destruction by bacteria is inhibited at low temperature. The organic material is transported by global circulation to warm tropical waters, where it is utilized to form particulate organic aggregates which serve as food for filter feeders.     

Patterns of houses and habitat loss from 1937 to 1999 in northern Wisconsin, USA.

Rural America is witnessing widespread housing development, which is to the detriment of the environment. It has been suggested to cluster houses so that their disturbance zones overlap and thus cause less habitat loss than is the case for dispersed development. Clustering houses makes intuitive sense, but few empirical studies have quantified the spatial pattern of houses in real landscapes, assessed changes in their patterns over time, and quantified the resulting habitat loss. We addressed three basic questions: (1) What are the spatial patterns of houses and how do they change over time; (2) How much habitat is lost due to houses, and how is this affected by spatial pattern of houses; and (3) What type of habitat is most affected by housing development. We mapped 27 419 houses from aerial photos for five time periods in 17 townships in northern Wisconsin and calculated the terrestrial land area remaining after buffering each house using 100- and 500-m disturbance zones. The number of houses increased by 353% between 1937 and 1999. Ripley's K test showed that houses were significantly clustered at all time periods and at all scales. Due to the clustering, the rate at which habitat was lost (176% and 55% for 100- and 500-m buffers, respectively) was substantially lower than housing growth rates, and most land area was undisturbed (95% and 61% for 100-m and 500-m buffers, respectively). Houses were strongly clustered within 100 m of lakes. Habitat loss was lowest in wetlands but reached up to 60% in deciduous forests. Our results are encouraging in that clustered development is common in northern Wisconsin, and habitat loss is thus limited. However, the concentration of development along lakeshores causes concern, because these may be critical habitats for many species. Conservation goals can only be met if policies promote clustered development and simultaneously steer development away from sensitive ecosystems.     

Investment in territorial defence depends on rearing environment in brown trout (Salmo trutta)

In many animals, territoriality will arise or cease depending on environmental factors such as intruder rate and resource availability. We investigated the effect of rearing environment on territorial behaviour in ~1.5-month-old brown trout. In the laboratory, wild-caught (reared at a low density) and hatchery-reared (high density) trout were allowed to defend a territory against a size-matched intruder reared in the same or the other environment. Because territorial behaviour should be relaxed at high-rearing densities, we hypothesized that hatchery-reared trout should value their territories less and therefore invest less in defence compared with wild-caught trout. However, in all cases, territory owners were more likely to win the contest and hatchery-reared trout were just as likely as wild-reared to win mixed contests. Furthermore, pairs of hatchery-reared trout initiated contests sooner, fought longer and were more aggressive during the contest compared with pairs of wild trout. When hatchery-reared owners met wild intruders, the contest ended sooner compared with when the roles were reversed. We conclude that territorial behaviour in brown trout is largely innate, but that the hatchery environment has promoted more aggressive individuals. These results suggest that hatchery-reared trout invest more time and energy to obtain the same contest success as wild trout. In conclusion, the lack of experience of territorial defence in a high-density rearing environment seems to reduce the efficiency of territorial behaviour. In turn, this may have negative consequences for the performance of released hatchery fish in the wild.