Life history evolution in cichlids 2: directional evolution of the trade-off between egg number and egg size

The negative relationship between offspring number and offspring size provides a classic example of the role of trade-offs in life history theory. However, the evolutionary transitions in egg size and clutch size that have produced this negative relationship are still largely unknown. Since body size may affect both of these traits, it would be helpful to understand how evolutionary changes in body size may have facilitated or constrained shifts in clutch and egg size. By using comparative methods with a database of life histories and a phylogeny of 222 genera of cichlid fishes, we investigated the order of evolutionary transitions in these traits in relation to each other. We found that the ancestral large-bodied cichlids first increased egg size, followed by a decrease in both body size and clutch size resulting in the common current combination of a small-bodied cichlid with a small clutch of large eggs. Furthermore, lineages that deviated from the negative relationship between clutch and egg size underwent different transitions in these traits according to their body size (large bodied genera have moved towards the large clutch/small egg end of the continuum and small bodied genera towards the small clutch/large egg end of the continuum) to reach the negative relationship between clutch size and egg size. Our results show that body size is highly important in shaping the negative relationship between clutch size and egg size.

Biology of extinction risk in marine fishes

We review interactions between extrinsic threats to marine fishes and intrinsic aspects of their biology that determine how populations and species respond to those threats. Information is available on the status of less than 5% of the world's approximately 15500 marine fish species, most of which are of commercial importance. By 2001, based on data from 98 North Atlantic and northeast Pacific populations, marine fishes had declined by a median 65% in breeding biomass from known historic levels; 28 populations had declined by more than 80%. Most of these declines would be sufficient to warrant a status of threatened with extinction under international threat criteria. However, this interpretation is highly controversial, in part because of a perception that marine fishes have a suite of life history characteristics, including high fecundity and large geographical ranges, which might confer greater resilience than that shown by terrestrial vertebrates. We review 15 comparative analyses that have tested for these and other life history correlates of vulnerability in marine fishes. The empirical evidence suggests that large body size and late maturity are the best predictors of vulnerability to fishing, regardless of whether differences among taxa in fishing mortality are controlled; there is no evidence that high fecundity confers increased resilience. The evidence reviewed here is of direct relevance to the diverse criteria used at global and national levels by various bodies to assess threat status of fishes. Simple life history traits can be incorporated directly into quantitative assessment criteria, or used to modify the conclusions of quantitative assessments, or used as preliminary screening criteria for assessment of the approximately 95% of marine fish species whose status has yet to be evaluated either by conservationists or fisheries scientists.

Climate Change and Distribution Shifts in Marine Fishes

We show that the distributions of both exploited and nonexploited North Sea fishes have responded markedly to recent increases in sea temperature, with nearly two-thirds of species shifting in mean latitude or depth or both over 25 years. For species with northerly or southerly range margins in the North Sea, half have shown boundary shifts with warming, and all but one shifted northward. Species with shifting distributions have faster life cycles and smaller body sizes than nonshifting species. Further temperature rises are likely to have profound impacts on commercial fisheries through continued shifts in distribution and alterations in community interactions.

Long-term behavioral assessment of guinea pigs following neonatal pneumoperitoneum

BACKGROUND

Using guinea pigs, we previously demonstrated that pneumoperitoneum during pregnancy produces behavioral deficits in the offspring. In the current study, the purpose was to determine if CO(2) pneumoperitoneum during the early postnatal period also produced behavioral anomalies.

METHODS

Following delivery, guinea pig pups were randomly assigned to one of three treatment groups: CO(2) pneumoperitoneum (P), laparotomy (L), or isolation control (I). Surgeries were performed on postnatal day (PND) 5 under isoflurane anesthesia; control pups were isolated from the dams for an equivalent period of time. On PNDs 10, 20, 40, and 60, behavior was assessed by monitoring locomotor and exploratory activity.

RESULTS

A total of 29 animals were studied. We observed no immediate morbidity or mortality and the manipulations did not appear to affect postnatal growth. On PND 10, pups in group P exhibited lower levels of locomotor activity compared to L and I neonates, but this difference resolved as the animals got older. Histologic assessment of the adult offspring brains revealed no evidence of neurologic injury.

CONCLUSION

These data suggest that unlike insufflation during pregnancy, neonatal pneumoperitoneum does not produce behavioral deficits.

Sexual selection explains Rensch's rule of size dimorphism in shorebirds

Sexual size dimorphism shows a remarkably widespread relationship to body size in the animal kingdom: within lineages, it decreases with size when females are the larger sex, but it increases with size when males are the larger sex. Here we demonstrate that this pattern, termed Rensch's rule, exists in shorebirds and allies (Charadriides), and it is determined by two components of sexual selection: the intensity of sexual selection acting on males and the agility of the males' display. These effects are interactive so that the effect of sexual selection on size dimorphism depends on male agility. As a control, we also examine dimorphism in bill length, which is a functionally selected trait. As such, dimorphism in bill length neither exhibits Rensch's rule nor is associated with sexual selection and display. Our results show that variation among taxa in the direction and magnitude of sexual size dimorphism, as manifested as Rensch's rule, can be explained by the interaction between the form and strength of sexual selection acting on each sex in relation to body size.

The role of macrophages in the removal of apoptotic B-cells in the sheep ileal Peyer's patch

In the process of generating the cells that populate the sheep's B-cell pool, the ileal Peyer's patch (PP) produces an immense number of B-cells and then destroys most of them by apoptosis. Rapid clearance of these apoptotic cells is essential for tissue homeostasis and for preventing pathology. Macrophages comprise a small percentage of cells in the follicles. They resemble macrophages found in other tissues and can be identified by the expression of MHC Class II and CD14. In this study, enriched macrophages co-cultured with apoptotic ileal PP cells showed increased DNA content as they ingested apoptotic cells. The higher the proportion of apoptotic cells in culture the greater the increase in DNA content of the macrophages. This occurred when B-cell apoptosis was initiated by a period in culture or in response to treating the animals with steroids. Thus, macrophages resident in the ileal PP follicle mediate the phagocytosis and removal of discarded B-cells.

Migration route and spawning area fidelity by North Sea plaice

Data from plaice, Pleuronectes platessa L., tagged with electronic data storage tags, were used to test whether these fishes exhibited migration route and spawning area fidelity in successive spawning seasons. Depth and temperature data were recorded for each fish over 365-512 days in the central North Sea and this information was used to reconstruct movements based on tidal locations. We discovered highly directed seasonal migrations from the winter spawning area south of a major topographical feature, Dogger Bank Tail End, to summer feeding grounds 250 km to the north in deep, cold, thermally stratified water. Our results show synchronous timing of migration, repeated pre- and post-spawning migration routes and 100% spawning area fidelity, including two individuals that returned to within 20 km of their previous season's spawning location. This is the first study to provide a complete reconstruction of annual migrations by individual fishes, showing strong homing behaviour along consistent migration routes.

Early postnatal behavior deficits after maternal carbon dioxide pneumoperitoneum during pregnancy

BACKGROUND

In this study, we tested the hypothesis that maternal pneumoperitoneum produces early postnatal behavior deficits in the offspring.

METHODS

Time-dated pregnant guinea pigs were exposed to 45 min of carbon dioxide (CO2) pneumoperitoneum at a pressure of 7 mmHg. There was no manipulation of the control animals. On postnatal days (PND) 10 and 20, the behavior of their offspring was assessed by monitoring the locomotor activity of each of the pups in a 1 x 1 m chamber demarcated into 100 squares. Locomotor data was log-transformed and expressed as mean values (SD).

RESULTS

At PND 10, pneumoperitoneum offspring exhibited significantly higher levels of locomotor activity than the offspring of controls (1.81 +/- 0.48 vs 1.33 +/- 0.78). The pneumoperitoneum pups continued to exhibit hyperactive behavior at PND 20 (1.83 +/- 0.72 vs 1.20 +/- 0.72).

CONCLUSIONS

Maternal pneumoperitoneum produces postnatal hyperactivity in guinea pig offspring, suggesting that there may be long-term consequences associated with the physiologic changes produced in the fetus during CO2 insufflation.

Directional changes in sexual size dimorphism in shorebirds, gulls and alcids

The Charadrii (shorebirds, gulls and alcids) are one of the most diverse avian groups from the point of view of sexual size dimorphism, exhibiting extremes in both male-biased and female-biased dimorphism, as well as monomorphism. In this study we use phylogenetic comparative analyses to investigate how size dimorphism has changed over evolutionary time, distinguishing between changes that have occurred in females and in males. Independent contrasts analyses show that both body mass and wing length have been more variable in males than in females. Directional analyses show that male-biased dimorphism has increased after inferred transitions towards more polygynous mating systems. There have been analogous increases in female-biased dimorphism after transitions towards more socially polyandrous mating systems. Changes in dimorphism in both directions are attributable to male body size changing more than female body size. We suggest that this might be because females are under stronger natural selection constraints related to fecundity. Taken together, our results suggest that the observed variation in dimorphism of Charadrii can be best explained by male body size responding more sensitively to variable sexual selection than female body size.

Extracellular glutamate levels and neuropathology in cerebral white matter following repeated umbilical cord occlusion in the near term fetal sheep

Umbilical cord occlusion causes fetal hypoxemia which can result in brain injury including damage to cerebral white matter. Excessive glutamate release may be involved in the damage process. This study examined the relation between extracellular glutamate levels in the cerebral white matter of the ovine fetus during and after intermittent umbilical cord occlusion and the degree of resultant fetal brain injury. Fetal sheep underwent surgery for chronic catheterisation and implantation of an intra-cerebral microdialysis probe at 130 days of gestation (term approximately 147 days). Four days after surgery (day 1), seven fetuses were subjected to 5x2 min umbilical cord occlusions, and on the following day (day 2) they were subjected to either 4 or 5x4 min umbilical cord occlusions; seven fetuses served as controls. Microdialysis samples were collected before, during and after the umbilical cord occlusions to determine extracellular glutamate levels in the cerebral white matter. Fetal blood gas status was measured and the fetal electrocorticogram was recorded continuously. During the periods of umbilical cord occlusions on both days 1 and 2, fetal arterial oxygen saturation, arterial partial pressure of oxygen and arterial pH decreased (P<0.05) while arterial partial pressure of carbon dioxide increased (P<0.05). All fetuses showed episodes of isoelectric electrocortical activity during umbilical cord occlusions on both days 1 and 2. In fetuses with patent microdialysis probes there were marked increases of glutamate efflux in the cerebral white matter following umbilical cord occlusion. Fetal brains were removed at autopsy on day 5 and subjected to histological assessment. Brain damage was observed in all fetuses exposed to cord occlusion, particularly in the periventricular white matter, with the most extensive damage occurring in the fetuses with the greatest increases in glutamate levels. We conclude that, in the unanesthetised fetus in utero, glutamatergic processes are associated with umbilical cord occlusion-induced brain damage in the cerebral white matter.

A new model of sheep Ig diversification: shifting the emphasis toward combinatorial mechanisms and away from hypermutation

The current model of Ig repertoire development in sheep focuses on the rearrangement of a small number (approximately 20) of Vlambda gene segments. It is believed that this limited combinatorial repertoire is then further diversified through postrearrangement somatic hypermutation. This process has been reported to introduce as many as 110 mutations/1000 nucleotides. In contrast, our data have that indicated somatic hypermutation may diversify the preimmune repertoire to a much lesser extent. We have identified 64 new Vlambda gene segments within the rearranged Ig repertoire. As a result, many of the unique nucleotide patterns thought to be the product of somatic hypermutation are actually hard-coded within the germline. We suggest that combinatorial rearrangement makes a much larger contribution, and somatic hypermutation makes a much smaller contribution to the generation of diversity within the sheep Ig repertoire than is currently acknowledged.

Life-history correlates of maximum population growth rates in marine fishes

Theory predicts that populations of animals with late maturity, low fecundity, large body size and low body growth rates will have low potential rates of population increase at low abundance. If this is true, then these traits may be used to predict the intrinsic rate of increase for species or populations, as well as extinction risks. We used life-history and population data for 63 stocks of commercially exploited fish species from the northeast Atlantic to test relationships between life-history parameters and the rate of population increase at low abundance. We used cross-taxonomic analyses among stocks and among species, and analyses that accounted for phylogenetic relationships. These analyses confirmed that large-bodied, slow-growing stocks and species had significantly lower rates of recruitment and adult production per spawning adult at low abundance. Furthermore, high ages at maturity were significantly correlated with low maximum recruit production. Contrary to expectation, fecundity was significantly negatively related to recruit production, due to its positive relationship with maximum body size. Our results support theoretical predictions, and suggest that a simply measured life-history parameter can provide a useful tool for predicting rates of recovery from low population abundance.

Adjustments of ejaculation rates in response to risk of sperm competition in a fish, the bitterling (Rhodeus sericeus)

Game theory models of sperm competition predict that within species, males should increase their sperm expenditure when they have one competitor, but decrease expenditure with increasing numbers of competitors. So far, there have been few tests or support for this prediction. Here, we show that males of a freshwater fish, the European bitterling, Rhodeus sericeus, do indeed adjust their ejaculation rate to the number of male competitors by first increasing and then decreasing their ejaculation rates as the number of competitors increases. However, this occurred only under restricted conditions. Specifically, the prediction was upheld as long as no female had deposited eggs in the live mussels that are used as spawning sites. After one or more females had spawned, males did not decrease their ejaculation rates with the number of competitors, but instead they became more aggressive. This indicates that decreased ejaculation rate and increased aggression are alternative responses to increased risk of sperm competition.

Life-history correlates of the evolution of live bearing in fishes

Selection for live bearing is thought to occur when the benefits of increasing offspring survival exceed the costs of reduced fecundity, mobility and the increased metabolic demands of carrying offspring throughout development. We present evidence that live bearing has evolved from egg laying 12 times in teleost (bony) fishes, bringing the total number of transitions to 21 to 22 times in all fishes, including elasmobranchs (sharks and rays). Live bearers produce larger offspring than egg layers in all of 13 independent comparisons for which data were available. However, contrary to our expectation there has not been a consistent reduction in fecundity; live bearers have fewer offspring in seven out of the 11 available comparisons. It was predicted that live bearers would have a larger body size, as this facilitates accommodation of developing offspring. This prediction was upheld in 14 out of 20 comparisons. However, this trend was driven by elasmobranchs, with large live bearers in seven out of eight comparisons. Thus, while the evolution of live bearing in elasmobranchs is correlated with predicted increases in offspring size and adult size, teleost live bearers do not have such a consistent suite of life-history correlates. This suggests that constraints or selection pressures on associated life histories may differ in live-bearing elasmobranchs and teleost fishes.

Evolutionary transitions in parental care and live bearing in vertebrates

We provide the first review of phylogenetic transitions in parental care and live bearing for a wide variety of vertebrates. This includes new analyses of both numbers of transitions and transition probabilities. These reveal numerous transitions by shorebirds and anurans toward uniparental care by either sex. Whereas most or all of the shorebird transitions were from biparental care, nearly all of the anuran transitions have been from no care, reflecting the prevalence of each form of care in basal lineages in each group. Teleost (bony) fishes are similar to anurans in displaying numerous transitions toward uniparental contributions by each sex. Whereas cichlid fishes have often evolved from biparental care to female care, other teleosts have usually switched from no care to male care. Taxa that have evolved exclusive male care without courtship-role reversal are characterized by male territoriality and low costs of care per brood. Males may therefore benefit from care through female preference of parental ability in these species. Primates show a high frequency of transitions from female care to biparental care, reflecting the prevalence of female care in basal lineages. In the numerous taxa that display live bearing by females, including teleosts, elasmobranchs, squamate reptiles and invertebrates, we find that live bearing has always evolved from a lack of care. Although the transition counts and probabilities will undoubtedly be refined as phylogenetic information and methodologies improve, the overall biases in these taxa should help to place adaptive hypotheses for the evolution of care into a stronger setting for understanding directions of change.

Retinopathy of prematurity: clinical aspects

There have been many major advances recently that have improved the identification and management of retinopathy of prematurity (ROP). This chapter describes the clinical features of ROP and then considers briefly the incidence and epidemiology of acute phase disease. This is followed by a discussion of the two ROP epidemics and ROP-induced disability in high, low and middle income countries, and how this has been impacted by treatment. The principles and specifics of screening for ROP are considered, focusing on certain topical issues such as whether one screening guideline suits all populations. Treatment has undergone several advances, so that now laser therapy has overtaken cryotherapy as the preferred mode of treatment, and treatment at an earlier stage is now being considered. Finally, the authors attempt to look into the future and wonder how the criteria for treatment will change, and whether innovations in ocular imaging will impact ROP screening in both high and middle income countries.

Intravenous magnesium sulfate does not increase ventricular CSF ionized magnesium concentration of patients with intracranial hypertension

Magnesium sulfate has attracted interest as a potential neuroprotectant but passage of magnesium ion into the central nervous system has not been well documented. For this study, we quantified plasma and cerebrospinal fluid (CSF) ionized magnesium concentration after systemic magnesium sulfate infusion in patients with intracranial hypertension. Patients ( N = 9) received an intravenous infusion of 5 g/20 mmol magnesium sulfate (125 mL of a 4% wt/vol solution) over 30 minutes. Before and after dosing, CSF (from an indwelling ventricular catheter) and blood samples were collected at hourly intervals. Ionized magnesium concentration in all samples was determined using an electrolyte analyzer. Baseline plasma and CSF ionized magnesium concentrations were 0.58 +/- 0.05 and 0.82 +/- 0.06 mmol/L, respectively. Intravenous magnesium sulfate infusion significantly increased plasma ionized magnesium concentration (peak, 0.89 +/- 0.11 mmol/L), but CSF magnesium levels did not change during the 4-hour study. Systemic administration of magnesium sulfate failed to increase CSF ionized magnesium concentration in patients with intracranial hypertension despite increasing plasma magnesium levels by >50%.