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The problem of whether haplodiploidy is responsible for the frequent evolution of eusociality in the Hymenoptera remains unresolved. The little-known "protected invasion hypothesis" posits that because a male will transmit a new allele for alloparental care to all his daughters under haplodiploidy, such an allele has a higher probability of spreading to fixation under haplodiploidy than under diploidy. This mechanism is investigated using the mating system and lifecycles ancestral to eusocial lineages. It is shown that although haplodiploidy increases the probability of fixation of a new allele, the effect is cancelled by a higher probability of the allele arising in a diploid population. However, the same effect of male haploidy results in a 30% lower threshold amount of reproductive help by a worker necessary to favor eusociality if the sex ratio of dispersing first-brood offspring remains even. This occurs because when first-brood daughters become workers, the sex ratio of dispersing first-brood offspring becomes male-biased, selecting for an overall female-biased first-brood sex ratio. Through this mechanism, haplodiploidy may favor eusociality in the absence of a female-biased sex ratio in dispersing reproductive offspring. The gene-centric approach used here reveals the critical role of male haploidy in structuring the social group.

Genomic imprinting is known from flowering plants and mammals but has not been confirmed for the Hymenoptera even though the eusocial Hymenoptera are prime candidates for this peculiar form of gene expression. Here, the kin selection theory of genomic imprinting is reviewed and applied to the eusocial Hymenoptera. The evidence for imprinting in eusocial Hymenoptera with the typical mode of reproduction, involving the sexual production of diploid female offspring, which develop into workers or gynes, and the arrhenotokous parthenogenesis of haploid males, is also reviewed briefly. However, the focus of this review is how atypical modes of reproduction, involving thelytokous parthenogenesis, hybridisation and androgenesis, may also select for imprinting. In particular, naturally occurring hybridisation in several genera of ants may provide useful tests of the role of kin selection in the evolution of imprinting. Hybridisation is expected to disrupt the coadaptation of antagonistically imprinted loci, and thus affect the phenotypes of hybrids. Some of the limited data available on hybrid worker reproduction and on colony sex ratios support predictions about patterns of imprinting derived from kin selection theory.

The evolution of effectively sterile workers in the aculeate Hymenoptera (ants, bees, and stinging wasps) requires that a female's life span largely overlap that of her daughters. The evolution of long nest foundress life spans in eusocial species from the short life spans of solitary species is investigated. Analyses that control for phylogeny show for the first time that foundress adult life span increases and first-brood offspring development time decreases with increasing colony size, resulting in the ratio of foundress adult life span to worker total life span increasing with increasing colony size. These patterns support the hypothesis that the reproductive division of labor increases with increasing colony size, explaining the evolution of effectively sterile workers in species with large colonies. However, there is a discrete increase in foundress adult life span in the transition from noneusociality to eusociality that is independent of colony size. An analysis of life history characters suggests that this increase is explained by nests being founded by multiple females and progressive feeding of larvae as they develop. A reduced rate of senescence of a dominant cofoundress may be selected as a plastic response to social status if high-risk tasks performed by subordinate cofoundresses reduce the dominant's extrinsic mortality rate. Multiple-foundress nests in which one female is responsible for most or all of the reproduction (semisociality) and in which foundresses are full sisters are favored by haplodiploidy, perhaps explaining why eusociality is so common in the Hymenoptera.

The demonstration of life span plasticity in natural populations would provide a powerful test of evolutionary theories of senescence. Plastic senescence is not easily explained by mutation accumulation or antagonistic pleiotropy but is a corollary of the disposable soma theory. The life span differences among castes of the eusocial Hymenoptera are potentially some of the most striking and extreme examples of life span plasticity. Although these differences are often assumed to be plastic, this has never been demonstrated conclusively because differences in life span may be caused by the proximate effects of different levels of environmental hazard experienced by castes. Here age-dependent and age-independent components of instantaneous mortality rates of the honey bee (

The classic evolutionary theory of aging posits that senescence evolves because the weakening of selection with age allows mutations with late-acting deleterious effects to accumulate. Because extrinsic mortality is an important cause of weakening selection, the central prediction of the theory has been that higher extrinsic mortality should lead to the evolution of a higher rate of senescence. However, the validity of this prediction has been questioned, even to the extent of suggesting that it is not a prediction of the theory at all, primarily on the basis that changes in population growth rate will compensate for changes in extrinsic mortality. The implication is that empiricists have been using the wrong prediction to test the theory. This claim is misleading, however, because it does not apply on an evolutionary timescale, when population size must be roughly constant. With a constant population size, Hamilton’s fitness sensitivities show that extrinsic mortality determines the rate at which the strength of selection declines with age, and thus determines the rate of senescence. The central prediction has been confirmed in the few controlled experiments with model organisms that have been conducted, but clearly this is an area ripe for further investigation.

The disruptive selection theory of the evolution of anisogamy posits that the evolution of a larger body or greater organismal complexity selects for a larger zygote, which in turn selects for larger gametes. This may provide the opportunity for one mating type to produce more numerous, small gametes, forcing the other mating type to produce fewer, large gametes. Predictions common to this and related theories have been partially upheld. Here, a prediction specific to the disruptive selection theory is derived from a previously published game‐theoretic model that represents the most complete description of the theory. The prediction, that the ratio of macrogamete to microgamete size should be above three for anisogamous species, is supported for the volvocine algae. A fully population genetic implementation of the model, involving mutation, genetic drift, and selection, is used to verify the game‐theoretic approach and accurately simulates the evolution of gamete sizes in anisogamous species. This model was extended to include a locus for gamete motility and shows that oogamy should evolve whenever there is costly motility. The classic twofold cost of sex may be derived from the fitness functions of these models, showing that this cost is ultimately due to genetic conflict.

Although the gamete competition theory remains the dominant explanation for the evolution of anisogamy, well-known exceptions to its predictions have raised doubts about the completeness of the theory. One of these exceptions is isogamy in large or complex species of green algae. Here, we show that this exception may be explained in a manner consistent with a game-theoretic extension of the original theory: a constraint on the minimum size of a gamete may prevent the evolution of continuously stable anisogamy. We show that in the volvocine algae, both gametes of isogamous species retain an intact chloroplast, whereas the chloroplast of the microgamete in anisogamous species is invariably degenerate. The chloroplast, which functions in photosynthesis and starch storage, may be necessary to provision a gamete for an extended period when gamete encounter rates are low. The single chloroplast accounts for most of the volume of a typical gamete, and thus may constrain the minimum size of a gamete, preventing the evolution of anisogamy. A prediction from this hypothesis, that isogametes should be larger than the microgametes of similar-size species, is confirmed for the volvocine algae. Our results support the gamete competition theory.

Pathogens adapt to antibody surveillance through amino acid replacements in targeted protein regions, or epitopes, that interfere with antibody binding. However, such escape mutations may exact a fitness cost due to impaired protein function. Here, it is hypothesized that the recurring generation of specific neutralizing antibodies to an epitope region as it evolves in response to antibody selection will cause amino acid reversions by releasing early escape mutations from immune selection. The plausibility of this hypothesis was tested with stochastic simulation of adaptation at the molecular sequence level in finite populations. Under the conditions of strong selection and weak mutation, the rates of allele fixation and amino acid reversion increased with population size and selection coefficients. These rates decreased with population size, however, if mutation became strong, because clonal interference reduced the rate of adaptation. The model successfully predicts the rate of reversion per allele fixation for an important human immunodeficiency virus type 1 (HIV-1) antibody epitope region. Therefore, antibody selection may generate complex adaptive dynamics.

Human immunodeficiency virus type 1 (HIV-1) undergoes a severe population bottleneck during sexual transmission and yet adapts extremely rapidly to the earliest immune responses. The bottleneck has been inferred to typically consist of a single genome, and typically eight amino acid mutations in viral proteins spread to fixation by the end of the early chronic phase of infection in response to selection by CD8+ T cells. Stochastic simulation was used to examine the effects of the transmission bottleneck and of potential interference among spreading immune-escape mutations on the adaptive dynamics of the virus in early infection. If major viral population genetic parameters are assigned realistic values that permit rapid adaptive evolution, then a bottleneck of a single genome is not inconsistent with the observed pattern of adaptive fixations. One requirement is strong selection by CD8+ T cells that decreases over time. Such selection may reduce effective population sizes at linked loci through genetic hitchhiking. However, this effect is predicted to be minor in early infection because the transmission bottleneck reduces the effective population size to such an extent that the resulting strong selection and weak mutation cause beneficial mutations to fix sequentially and thus avoid interference.

The mutational landscape model of adaptive sequence evolution has been used to explain an unexpected strong positive linear relationship between marginal fitness and mean site-specific amino acid frequency in the functionally important HIV-1 gp120 V3 protein region. The model predicts a positive linear relationship between the probability that a particular beneficial allele, among several, is the next to spread to fixation during an adaptive walk, its transition probability, and the allele's selection coefficient. Here, stochastic simulation is used to confirm the intuition that the linear relationship between transition probabilities and selection coefficients, predicted by the model, should, under fluctuating selection, produce a linear relationship between allele frequency, averaged across populations, and fitness. In addition, these relationships hold for the effective population size and mutation rate of HIV-1 and for the moderately strong selection observed for V3. A survey of the strength of mutation for diverse organisms suggests that these relationships may be widely applicable.

The frequently reported amino acid covariation of the highly polymorphic human immunodeficiency virus type 1 (HIV-1) exterior envelope glycoprotein V3 region has been assumed to reflect fitness epistasis between residues. However, nonrandom association of amino acids, or linkage disequilibrium, has many possible causes, including population subdivision. If the amino acids at a set of sequence sites differ in frequencies between subpopulations, then analysis of the whole population may reveal linkage disequilibrium even if it does not exist in any subpopulation. HIV-1 has a complex population structure, and the effects of this structure on linkage disequilibrium were investigated by estimating within- and among-subpopulation components of variance in linkage disequilibrium. The amino acid covariation previously reported is explained by differences in amino acid frequencies among virus subpopulations in different patients and by nonsystematic disequilibrium among patients. Disequilibrium within patients appears to be entirely due to differences in amino acid frequencies among sampling time points and among chemokine coreceptor usage phenotypes of virus particles, but not source tissues. Positive selection explains differences in allele frequencies among time points and phenotypes, indicating that these differences are adaptive rather than due to genetic drift. However, the absence of a correlation between linkage disequilibrium and phenotype suggests that fitness epistasis is an unlikely cause of disequilibrium. Indeed, when population structure is removed by analyzing sequences from a single time point and phenotype, no disequilibrium is detectable within patients. These results caution against interpreting amino acid covariation and coevolution as evidence for fitness epistasis.

Two MHC class II loci, DAB (a classical class II locus) and DXB (putatively a non-classical class II locus), were sequenced in samples of individuals from two populations of swordtail fish, Xiphophorus multilineatus and X. pygmaeus. The DAB locus showed higher levels of genetic variation in the B1-encoding region, (putative binding region) than the DXB locus. We used two methods to investigate d(N)/d(S) ratios. The results from a maximum likelihood method based on phylogenetic relationships indicated positive selection on the B1 region of DAB (this method could not be used on DXB). Results from a coalescent-based method also showed evidence for positive selection in the B1 region of DAB, but only weak evidence for selection on the DXB. Further analyses indicated that recombination is an important source of variation in the B1 region of DAB, but has a relatively small effect on DXB. Overall, our results were consistent with the hypothesis that the DAB locus is under positive selection driven by antagonistic coevolution, and that the DXB locus plays the role of a non-classical MHC II locus. We also used simulations to investigate the presence of an elevated synonymous substitution rate in the binding region. The simulations revealed that the elevated rate could be caused by an interaction between positive selection and codon bias.

Analysis of the intensely studied HIV-1 gp120 V3 protein region reveals that the among-population mean site-specific frequency of an amino acid is a measure of its relative marginal fitness. This surprising result may arise if populations are displaced from mutation–selection equilibrium by fluctuating selection and if the probability of fixation of a beneficial amino acid is proportional to its selection coefficient.

Recent evidence of the evolutionary adaptation of HIV-1 to the specific immune system is reviewed. Longitudinal studies of patients show that a neutralizing antibody (NAb) response specific to autologous virus is detectable within 1-2 months of infection and that viral variants resistant to neutralization arise and spread in the viral population within the subsequent three months, and that this general pattern is repeated. There is strong evidence that amino acid replacements in gp120 glycan-binding motifs affect viral sensitivity to neutralization and are selected by NAbs. Longitudinal studies of humans have also provided good evidence of amino acid replacements in cytotoxic T lymphocyte (CTL) epitopes that allow the virus to escape detection by CTLs. But, the clearest evidence of adaptation to CTL surveillance at the molecular level comes from experiments with SIV-infected rhesus macaques. These show unequivocally that amino acid replacements in CTL epitopes are the result of positive selection and that these escape mutants have a lower class I major histocompatibility complex (MHC) binding affinity or are less likely to be recognized by CTLs than non-escape variants. To improve our ability to predict HIV's evolutionary responses to selection by the specific immune system it is suggested that future work focus on the details of the adaptive response to antibody surveillance, the temporal dynamics of specific immune responses, the relative importance of antibody and CTL selection, and the effects of superinfection, viral recombination, and viral protein functional constraints on immune escape.

The trill vocalization is given by eastern chipmunks (Tamias striatus) when being pursued by a predator. To examine the adaptive significance of this vocalization, we assessed the effects of sex, age, and distance from the burrow on the occurrence of the call. Chipmunks were released either 10 or 100 m from their burrow and chased by an experimenter to simulate a terrestrial predator. We found that adult females trill more often when released 10 m from their burrow (67% of 24 chases) than when released 100 m from their burrow (14% of 21 chases). Adult males, on the other hand, showed no significant difference in their probability of trilling based on the distance from their burrows (45% of 20 chases at 10 m and 55% of 20 chases at 100 m). Adult females trilled more than adult males when released 10 m from their burrow (67% compared with 45%) but less than males when released 100 m from their burrow (14% compared with 55%). Juvenile females only trilled when released 10 m from their burrows (45% of 11 chases), and juvenile males did not trill at all. We attributed sex, age, and location differences in giving the trill vocalization to the effects of kin selection on antipredator behavior.

Tat-specific cytotoxic T cells have previously been shown to exert positive Darwinian selection favoring amino acid replacements of an epitope of simian immunodeficiency virus (SIV). The region of the tat gene encoding this epitope falls within a region of overlap between the tat and vpr reading frames, and nonsynonymous nucleotide substitutions in the tat reading frame were found to occur disproportionately in such a way as to cause synonymous changes in the vpr reading frame. Comparison of published complete SIV genomes showed Tat to be the least conserved at the amino acid level of nine proteins encoded by the virus, while Vpr was one of the most conserved. Numerous parallel amino acid changes occurred within the Tat epitope independently in different monkeys, and purifying selection on the vpr reading frame, by limiting acceptable nonsynonymous substitutions in the tat reading frame, evidently has enhanced the probability of parallel evolution.

The fact that there are four homeobox (Hox) clusters in most vertebrates but only one in invertebrates is often cited as evidence for the hypothesis that two rounds of genome duplication by polyploidization occurred early in vertebrate history. In addition, it has been observed in humans and other mammals that numerous gene families include paralogs on two or more of the fourHox-bearing chromosomes (the chromosomes bearing theHox clusters; i.e., human chromosomes 2, 7, 12, and 17), and the existence of these paralogs has been taken as evidence that these genes were duplicated along with the Hox clusters by polyploidization. We tested this hypothesis by phylogenetic analysis of 42 gene families including members on two or more of the humanHox-bearing chromosomes. In 32 of these families there was evidence against the hypothesis that gene duplication occurred simultaneously with duplication of the Hox clusters. Phylogenies of 14 families supported the occurrence of one or more gene duplications before the origin of vertebrates, and of 15 gene duplication times estimated for gene families evolving in a clock-like manner, only six were dated to the same time period early in vertebrate history during which the Hox clusters duplicated. Furthermore, of gene families duplicated around the same time as the Hoxclusters, the majority showed topologies inconsistent with their having duplicated simultaneously with the Hox clusters. The results thus indicate that ancient events of genome duplication, if they occurred at all, did not play an important role in structuring the mammalian Hox-bearing chromosomes.

A wide variety of higher taxa show right‐skewed frequency distributions of species' body sizes, and a negative relationship is often found between the number of species within a taxonomic group and its mean size. These patterns may arise from essentially random cladogenesis and extinction, from the tendency of organisms to anagenetically track a relatively small optimal size, or from high rates of cladogenesis at relatively small sizes. We used body mass data for about 65% of the world's mammal species to test the predictions of these alternative mechanisms. Using phylogenetically independent contrasts to control for phylogeny and clade age, we found that although size does not appear to be a general correlate of diversity, large radiations of species do tend to be small bodied. This pattern seems most consistent with the hypothesis that the number of niches is potentially greatest for small‐bodied taxa.

Women with BRCA1/2 mutations have a significantly higher lifetime risk of developing breast or ovarian cancer. We suggest that female mutation carriers may have improved fitness owing to enhanced fertility relative to non-carriers. Here we show that women who are carriers of BRCA1/2 mutations living in natural fertility conditions have excess fertility as well as excess post-reproductive mortality in relation to controls. Individuals who tested positive for BRCA1/2 mutations who linked into multi-generational pedigrees within the Utah Population Database were used to identify putative obligate carriers. We find that women born before 1930 who are mutation carriers have significantly more children than controls and have excess post-reproductive mortality risks. They also have shorter birth intervals and end child-bearing later than controls. For contemporary women tested directly for BRCA1/2 mutations, an era when modern contraceptives are available, differences in fertility and mortality persist but are attenuated. Our findings suggest the need to re-examine the wider role played by BRCA1/2 mutations. Elevated fertility of female mutation carriers indicates that they are more fecund despite their elevated post-reproductive mortality risks.

Since European badgers (Meles meles L.) form non-cooperative groups in parts of their geographic range, but are solitary elsewhere, their social systems have been at the centre of a debate about the evolution of group living in the Carnivora. In a recent review of models of non-cooperative sociality, Woodroffe and Macdonald (1993) presented evidence in favour of two hypotheses, which suggested that badger groups might form because either the distribution of blocks of foodrich habitat, or the economics of excavating new setts, prevented the division of group territories into individual territories. We present data upon the response of badger spatial organisation to a reduction in food-patch dispersion, brought about by the conversion of carthwormpoor arable land to earthworm-rich pasture over a 15-year period. This change in the distribution of earthworm-rich habitats was accompanied by territory fission, facilitated by the excavation of new setts. This indicates that the availability of sett sites had not constrained territory size at the start of the study. However, sett distribution did define the size and configuration of the daughter territories. We also show that variation among territories in the availability of food-rich habitats was reflected in the reproductive rates and body weights of the groups that inhabited them, although there was no detectable effect upon group size.

Fitness epistasis, the interaction among alleles at different loci in their effects on fitness, has potentially important consequences for adaptive evolution. We investigated fitness epistasis among amino acids of a functionally important region of the human immunodeficiency virus type 1 (HIV-1) exterior envelope glycoprotein (gp120). Seven mutations putatively involved in the adaptation of the second conserved to third variable protein region (C2–V3) to the use of an alternative host-cell chemokine coreceptor (CXCR4) for cell entry were engineered singly and in combinations on the wild-type genetic background and their effects on viral infectivity were measured. Epistasis was found to be common and complex, involving not only pairwise interactions, but also higher-order interactions. Interactions could also be surprisingly strong, changing fitness by more than 9 orders of magnitude, which is explained by some single mutations being practically lethal. A consequence of the observed epistasis is that many of the minimum-length mutational trajectories between the wild type and the mutant with highest fitness on cells expressing the alternative coreceptor are selectively inaccessible. These results may help explain the difficulty of evolving viruses that use the alternative coreceptor in culture and the delayed evolution of this phenotype in natural infection. Knowledge of common, complex, and strong fitness interactions among amino acids is necessary for a full understanding of protein evolution.

Antagonism between the sexual and vegetative life cycles of eukaryotes is the most fundamental assumption of the theory of sexual selection. A trade-off between sexual competence and vegetative growth rate is expected from life-history theory, which predicts a negative genetic correlation between any two components of fitness that together define total fitness. Alternatively, intra-sexual competition or mate choice may create a positive correlation between vegetative growth and mating success. We have described the nature of the genetic correlation between mating efficiency and vegetative growth rate in the unicellular, facultatively sexual, chlorophyte alga Chlamydomonas reinhardtii. By selecting for mating efficiency and measuring the correlated response in vegetative growth rate, we found a negative genetic correlation between fitness components, as predicted by life-history theory. This is the first demonstration of a net viability cost of sexual selection.

The form of the neutralizing antibody response to human immunodeficiency virus type 1 (HIV-1) and the evolutionary response by the virus are poorly understood. In order for a virus particle (virion) to infect a cell, exterior envelope glycoprotein (gp120) molecules on the virion’s surface must interact with receptors on the cell’s surface. Antibodies that bind to gp120 may neutralize a virion by interfering with these interactions. Therefore, gp120 is expected to evolve in response to selection by both cell-surface receptors and antibodies. The rate of such adaptation and the constraints imposed by a response to one selective force on the response to the other are unknown. Here, I describe a simulation modeling approach to these problems. The population of viral genomes infecting a single patient is represented by the intensely studied third variable (V3) region of gp120, the main determinant of which chemokine coreceptor a virion uses to enter a cell, and an important target of neutralizing antibodies. Mutation and recombination are applied by realistically simulating the viral replication cycle. Selection by chemokine coreceptors is simulated by taking advantage of the fact that mean site-specific amino acid frequencies are measures of the site-specific marginal fitnesses of amino acids in relation to coreceptor interactions. Selection by antibodies is imposed by simulating the affinity maturation of B-cell lineages that produce neutralizing antibodies to HIV-1 V3. These simulations make clear predictions about the functional cost of adaptation to antibody surveillance, which may help explain the pattern of chemokine coreceptor usage by HIV-1.

BACKGROUND Furosemide is usually administered by the oral or intravenous route to cardiac patients with hypertension and heart failure, as well as edema. Occasionally, furosemide cannot be administered by these routes. OBJECTIVE To evaluate the diuretic/natriuretic efficacy of subcutaneously administered furosemide in healthy volunteers. METHODS This single-center, double-blind, placebo-controlled, randomized, crossover pilot study compared the diuretic effect of subcutaneously administered furosemide and NaCl 0.9% (placebo) in 12 healthy volunteers. The study was conducted over 5 days. Baseline values were determined on day 1. On days 3 and 5, each volunteer was injected with either furosemide 20 mg (2 mL) or 2 mL of placebo subcutaneously. A washout period occurred on day 4. Fluid and dietary intake were controlled on all 3 data collection days. Primary outcome measures consisted of urine volume voided, urine sodium concentration, onset time and volume of initial urine output, and number of voids during 8 hours of urine collection. RESULTS All outcomes demonstrated statistically significant differences when treatment and placebo groups were compared (p < 0.05). Adverse effects most commonly reported by the participants were minor and included transient burning and stinging at the injection site. CONCLUSIONS This study demonstrates that subcutaneously administered furosemide is a viable alternative when the oral or intravenous route of administration is not desirable or possible in humans. However, the results of this study need to be corroborated in various patient populations.

Exoenzyme S (ExoS) is translocated into eukaryotic cells by the type III secretory process and has been hypothesized to function in conjunction with other virulence factors in the pathogenesis of Pseudomonas aeruginosa . To gain further understanding of how ExoS might contribute to P. aeruginosa survival and virulence, ExoS expression and the structural gene sequence were determined in P. aeruginosa soil isolates and compared with ExoS of clinical isolates. Significantly higher levels of ExoS ADP-ribosyltransferase (ADPRT) activity were detected in culture supernatants of soil isolates compared to those of clinical isolates. The higher levels of ADPRT activity of soil isolates reflected both the increased production of ExoS and the production of ExoS having a higher specific activity. ExoS structural gene sequence comparisons found the gene to be highly conserved among soil and clinical isolates, with the greatest number of nonsynonymous substitutions occurring within the region of ExoS encoding GAP function. The lack of amino acid changes in the ADPRT region in association with a higher specific activity implies that other factors produced by P. aeruginosa or residues outside the ADPRT region are affecting ExoS ADPRT activity. The data are consistent with ExoS being integral to P. aeruginosa survival in the soil and suggest that, in the transition of P. aeruginosa from the soil to certain clinical settings, the loss of ExoS expression is favored.

Cytotoxic T-lymphocyte (CTL) responses to human immunodeficiency virus arise early after infection, but ultimately fail to prevent progression to AIDS. Human immunodeficiency virus may evade the CTL response by accumulating amino-acid replacements within CTL epitopes. We studied 10 CTL epitopes during the course of simian immunodeficiency virus disease progression in three related macaques. All 10 of these CTL epitopes accumulated amino-acid replacements and showed evidence of positive selection by the time the macaques died. Many of the amino-acid replacements in these epitopes reduced or eliminated major histocompatibility complex class I binding and/or CTL recognition. These findings strongly support the CTL 'escape' hypothesis.

The commercial sea cucumber Parastichopus californicus was tagged in situ, and its daily summer activity patterns followed over periods of up to two months. On bedrock covered with shell rubble, cobbles, and boulders, P. californicus crawled an average of 3.9 m/d. Long term movement on gently sloping substrata showed no directional bias. Tidal currents in the study areas had no influence upon either orientation or locomotory direction. On vertical rock surfaces, P. californicus has a negative geotropic orientation which we conclude is associated with opportunistic suspension feeding. On horizontal substrata, feeding and locomotory behaviour in P. californicus are simultaneous activities, and we suggest that the apparent random activity patterns in these sea cucumbers is mediated by an evenly distributed and renewable source of detrital food.

Of three length classes of herring, Clupea harengus (30–35, 20–25, and [Formula: see text] total length), fed to a captive harbor seal, Phoca vitulina, otoliths were recovered only from herring 30–35 cm long; of these otoliths only 4% were recovered. Using surface area to volume ratios of otoliths, other fish species were predicted to be similarly underrepresented in scats. After digestion, otoliths showed fewer annuli and a reduction in length and width. Herring otoliths in harbor seal scats indicated the consumption of large herring ([Formula: see text] total length) only and could not be used to estimate numbers of prey consumed. The partial digestion of herring otoliths will result in underestimates of fish age, length, and weight if calculations are based on standard relationships between these parameters and measurements from undigested otoliths.