Revisiting the cost of carnivory in mammals.

Predator-prey relationships play a key role in the evolution and ecology of carnivores. An understanding of predator-prey relationships and how this differs across species and environments provides information on how carnivorous strategies have evolved and how they may change in response to environmental change. We aim to determine how mammals overcame the challenges of living within the marine environment; specifically, how this altered predator-prey body mass relationships relative to terrestrial mammals. Using predator and prey mass data collected from the literature, we applied phylogenetic piecewise regressions to investigate the relationship between predator and prey size across carnivorous mammals (51 terrestrial and 56 marine mammals). We demonstrate that carnivorous mammals have four broad dietary groups: small marine carnivores (< 11 000 kg) and small terrestrial carnivores (< 11 kg) feed on prey less than 5 kg and 2 kg, respectively. On average, large marine carnivores (> 11 000 kg) feed on prey equal to 0.01% of the carnivore's body size, compared to 45% or greater in large terrestrial carnivores (> 11 kg). We propose that differences in prey availability, and the relative ease of processing large prey in the terrestrial environment and small prey in marine environment, have led to the evolution of these novel foraging behaviours. Our results provide important insights into the selection pressures that may have been faced by early marine mammals and ultimately led to the evolution of a range of feeding strategies and predatory behaviours.

Ornament size and colour as alternative strategies for effective communication in gliding lizards.

Sexual ornamentation needs to be conspicuous to be effective in attracting potential mates and defending territories and indeed, a multitude of ways exists to achieve this. Two principal mechanisms for increasing conspicuousness are to increase the ornament's colour or brightness contrast against the background and to increase the size of the ornament. We assessed the relationship between the colour and size of the dewlap, a large extendible throat-fan, across a range of species of gliding lizards (Agamidae; genus Draco) from Malaysia and the Philippines. We found a negative relationship across species between colour contrast against the background and dewlap size in males, but not in females, suggesting that males of different species use increasing colour contrast and dewlap size as alternative strategies for effective communication. Male dewlap size also increases with increasing sexual size dimorphism, and dewlap colour and brightness contrast increase with increasing sexual dichromatism in colour and brightness, respectively, suggesting that sexual selection may act on both dewlap size and colour. We further found evidence that relative predation intensity, as measured from predator attacks on models placed in the field, may play a role in the choice of strategy (high chromatic contrast or large dewlap area) a species employs. More broadly, these results highlight that each component in a signal (such as colour or size) may be influenced by different selection pressures and that by assessing components individually, we can gain a greater understanding of the evolution of signal diversity.

Repeated evolution of exaggerated dewlaps and other throat morphology in lizards.

The existence of elaborate ornamental structures in males is often assumed to reflect the outcome of female mate choice for showy males. However, female mate choice appears weak in many iguanian lizards, but males still exhibit an array of ornament-like structures around the throat. We performed a phylogenetic comparative study to assess whether these structures have originated in response to male-male competition or the need for improved signal efficiency in visually difficult environments. We found little evidence for the influence of male-male competition. Instead, forest species were more likely to exhibit colourful throat appendages than species living in open habitats, suggesting selection for signal efficiency. On at least three independent occasions, throat ornamentation has become further elaborated into a large, conspicuously coloured moving dewlap. Although the function of the dewlap is convergent, the underlying hyoid apparatus has evolved very differently, revealing the same adaptive outcome has been achieved through multiple evolutionary trajectories. More generally, our findings highlight that extravagant, ornament-like morphology can evolve in males without the direct influence of female mate choice and that failure to consider alternative hypotheses for the evolution of these structures can obscure the true origins of signal diversity among closely related taxa.

Marked colour divergence in the gliding membranes of a tropical lizard mirrors population differences in the colour of falling leaves.

Populations of the Bornean gliding lizard, Draco cornutus, differ markedly in the colour of their gliding membranes. They also differ in local vegetation type (mangrove forest versus lowland rainforest) and consequently, the colour of falling leaves (red and brown/black in mangrove versus green, brown and black in rainforest). We show that the gliding membranes of these lizards closely match the colours of freshly fallen leaves in the local habitat as they appear to the visual system of birds (their probable predators). Furthermore, gliding membranes more closely resembled colours of local fallen leaves than standing foliage or fallen leaves in the other population's habitat. This suggests that the two populations have diverged in gliding membrane coloration to match the colours of their local falling leaves, and that mimicking falling leaves is an adaptation that functions to reduce predation by birds.

Key innovations and island colonization as engines of evolutionary diversification: a comparative test with the Australasian diplodactyloid geckos.

The acquisition of key innovations and the invasion of new areas constitute two major processes that facilitate ecological opportunity and subsequent evolutionary diversification. Using a major lizard radiation as a model, the Australasian diplodactyloid geckos, we explored the effects of two key innovations (adhesive toepads and a snake-like phenotype) and the invasion of new environments (island colonization) in promoting the evolution of phenotypic and species diversity. We found no evidence that toepads had significantly increased evolutionary diversification, which challenges the common assumption that the evolution of toepads has been responsible for the extensive radiation of geckos. In contrast, a snakelike phenotype was associated with increased rates of body size evolution and, to a lesser extent, species diversification. However, the clearest impact on evolutionary diversification has been the colonization of New Zealand and New Caledonia, which were associated with increased rates of both body size evolution and species diversification. This highlights that colonizing new environments can drive adaptive diversification in conjunction or independently of the evolution of a key innovation. Studies wishing to confirm the putative link between a key innovation and subsequent evolutionary diversification must therefore show that it has been the acquisition of an innovation specifically, not the colonization of new areas more generally, that has prompted diversification.

Historical contingency and behavioural divergence in territorial Anolis lizards.

The extent that evolution - including adaptation - is historically contingent (dependent on past events) has often been hotly debated, but is still poorly understood. In particular, there are little data on the degree that behaviour, an aspect of the phenotype that is strongly linked to contemporary environments (social or physical), retains the imprint of evolutionary history. In this study, I examined whether differences in the design of the territorial displays among species of Caribbean Anolis lizards reflect island-specific selection regimes, or historically contingent predispositions associated with different clade histories. Adult males advertise territory ownership using a series of headbobs and dewlap extensions, bouts of which vary in duration among species. When display durations were mapped onto the Anolis phylogeny, prominent differences between species belonging to the Western and Eastern Caribbean radiations were apparent. Statistical analyses confirmed that species differences in the duration of headbob displays, and to some extent the duration of dewlap extensions, were historically contingent. The unique evolutionary histories of each clade have seemingly had a profound effect on the subsequent direction of display evolution among descendent taxa. These results combined with those from previous studies on these lizards show that past history can have an important impact on the type of behaviour exhibited by species today, to the point that adaptive evolution can proceed quite differently in lineages originating from different evolutionary starting points.

Fossils and phylogeny uncover the evolutionary history of a unique antipredator behaviour.

Recently, two squirrel species (Spermophilus spp.) were discovered to anoint their bodies with rattlesnake scent as a means of concealing their odour from these chemosensory predators. In this study, we tested multiple species with predator scents (rattlesnake and weasel) to determine the prevalence of scent application across the squirrel phylogeny. We reconstructed the evolutionary history of the behaviour using a phylogenetic analysis and fossil records of historic predator co-occurrence. Squirrels with historical and current rattlesnake co-occurrence all applied rattlesnake scent, whereas no relationship existed between weasel scent application and either weasel or rattlesnake co-occurrence. This was surprising because experimental tests confirmed rattlesnake and weasel scent were both effective at masking prey odour from hunting rattlesnakes (the primary predator of squirrels). Ancestral reconstructions and fossil data suggest predator scent application in squirrels is ancient in origin, arising before co-occurrences with rattlesnakes or weasels in response to some other, now extinct, chemosensory predator.

Ornament evolution in dragon lizards: multiple gains and widespread losses reveal a complex history of evolutionary change.

The expression in females of ornaments thought to be the target of sexual selection in males is a long-standing puzzle. Two main hypotheses are proposed to account for the existence of conspicuous ornaments in both sexes (mutual ornamentation): genetic correlation between the sexes and sexual selection on females as well as males. We examined the pattern of ornament gains and losses in 240 species of dragon lizards (Agamidae) in order to elucidate the relative contribution of these two factors in the evolution of mutual ornamentation. In addition, we tested whether the type of shelter used by lizards to avoid predators predicts the evolutionary loss or constraint of ornament expression. We found evidence that the origin of female ornaments is broadly consistent with the predictions of the genetic correlation hypothesis. Ornaments appear congruently in both sexes with some lineages subsequently evolving male biased sexual dimorphism, apparently through the process of natural selection for reduced ornamentation in females. Nevertheless, ornaments have also frequently evolved in both sexes independently. This suggests that genetic correlations are potentially weak for several lineages and sexual selection on females is responsible for at least some evolutionary change in this group. Unexpectedly, we found that the evolutionary loss of some ornaments is concentrated more in males than females and this trend cannot be fully explained by our measures of natural selection.

Individual, sexual, seasonal, and temporal variation in the amount of sagebrush lizard scent marks.

Although many animals deposit scent marks, previous studies have focused almost entirely on rodents or on the chemical structure of the signal. Here, we study the quantity and temporal pattern of chemical deposition by the territorial sagebrush lizard Sceloporus graciosus, measuring both femoral pore and fecal deposits. Specifically, we tested whether variation in deposition is a good cue of individual and sexual identity and/or whether it is more closely associated with body size and reproductive state, indicators of physiological condition. The results support the latter hypothesis. We found that although the amount of fluid deposited on a single perch (rarely quantified in mammals) carries little information on individual or sexual identity, it reflects the physiological condition and reproductive state of individual lizards and is replenished on a roughly weekly cycle, potentially providing additional information on the producer's activity level. The amount of deposition may thus provide important information to chemical receivers making mate choice and territorial defense decisions. The results further suggest that seasonal increases in gland production allow lizards to mark more sites rather than to influence the quality of the signal on a single perch.

Intrasexual selection predicts the evolution of signal complexity in lizards.

Sexual selection has often been invoked in explaining extravagant morphological and behavioural adaptations that function to increase mating success. Much is known about the effects of intersexual selection, which operates through female mate choice, in shaping animal signals. The role of intrasexual selection has been less clear. We report on the first evidence for the coevolution of signal complexity and sexual size dimorphism (SSD), which is characteristically produced by high levels of male male competition. We used two complementary comparative methods in order to reveal that the use of complex signals is associated with SSD in extant species and that historical increases in complexity have occurred in regions of a phylogenetic tree characterized by high levels of pre-existing size dimorphism. We suggest that signal complexity has evolved in order to improve opponent assessment under conditions of high male male competition. Our findings suggest that intrasexual selection may play an important and previously underestimated role in the evolution of communicative systems.

Comparative expression analysis of the genes encoding polypyrimidine tract binding protein (PTB) and its neural homologue (brPTB) in prenatal and postnatal mouse brain.

The polypyrimidine tract binding protein (PTB) and its recently discovered homologue brain-enriched PTB (brPTB) are RNA binding proteins involved in the control of alternative splicing. We have characterized expression patterns of the PTB and brPTB in course of mouse brain development, using mRNA in situ hybridization. PTB is expressed in choroid plexi and ependyma at all the stages of development and temporarily in the mantle layer of migrating neuroblasts of fore-, mid- and hindbrain and in the external granular layer of cerebellum. In the neurons of adult mouse cerebrum and cerebellum expression of PTB is undetectable. In contrast to this, brPTB is expressed ubiquitously in neuroblasts of various parts of embryonic brain and in the differentiated neurons of postnatal cerebrum and cerebellum. brPTB mRNA is not observed in choroid plexi and ependymal layer. Thus, in the embryonic brain expression patterns of PTB and brPTB overlap, but in the course of brain development the patterns become complementary to each other.

Activation of CPP32 during apoptosis of neurons and astrocytes.

Members of the interleukin-1 beta-converting enzyme (ICE)/CED-3 protease family have been implicated in apoptosis in both vertebrates and invertebrates. Using primary culture methods, we report that neurons and astrocytes require the activity of the ICE/CED-3 family of proteases to undergo apoptosis induced by staurosporine, ceramide, and serum-free media. We show that specific inhibitors of ICE/CED-3 proteases can inhibit apoptosis and that cytosolic fractions from apoptosing neurons, but not healthy cells, induced apoptosis in a cell-free system. Cell extracts from neurons induced to undergo apoptosis contained ICE/ CED-3 protease activity. To determine which member of the ICE/CED-3 family was activated in neurons and astrocytes during apoptosis, we developed a novel affinity-labeling technique that labeled the active site cysteine and identified a 17-kDa subunit of the activated protease. The affinity-labeled 17-kDa protease subunit shares antigenic and molecular mass identity with the processed form of CPP32 on immunoblots, suggesting that CPP32 may be the principal effector in the apoptotic pathway in neurons and astrocytes. In time-course experiments, the activation of CPP32 preceded the detection of PARP cleavage and DNA laddering, suggesting that processing of CPP32 is a very early event in apoptosis of neurons and astrocytes and may be involved in the proteolytic action on specific cellular targets. The affinity-labeling technique developed and used in this report with neural cells allows for the sensitive detection, purification, and identification of ICE/CED-3 proteases that may be activated in other cells types under a variety of conditions, including certain diseased states.

The cysteine proteinase gene cprG in Dictyostelium discoideum has a serine-rich domain that contains GlcNAc-1-P.

A lysosomal cysteine proteinase called proteinase-1 is the major proteolytic enzyme in vegetative cells of Dictyostelium discoideum. This phosphoglycosylated protein contains multiple residues of GlcNAc-1-P linked to peptidyl serines. Here we report the cloning, structure, and expression of its cDNA (cprG). Another cDNA (cprF) closely related to cprG was also cloned and characterized. mRNAs of both genes are present during the vegetative phase and decrease in developing cells. However, the level of cprG mRNA is about 100-fold higher than that of cprF. The predicted protein products of both genes contain a unique serine-rich domain that was previously found only in two Dictyostelium proteinases (CP4 and CP5) that also carry a GlcNAc-1-P-Ser modification. The cprG product, renamed CP7, was tagged with the FLAG-epitope (FLAG-CP7) and shown to bind to cystatin, a highly specific inhibitor of cysteine proteinases. The FLAG-CP7 product also contained both N-linked oligosaccharides and GlcNAc-1-P. Deletion of the serine-rich domain from FLAG-CP7 yields a product that still binds to cystatin, but no longer carries GlcNAc-1-P. This finding supports the idea that the GlcNAc-1-P residues are normally added to the serine-rich domain, found only in vegetative Dictyostelium cysteine proteinases.

Bcl-2 expression in neural cells blocks activation of ICE/CED-3 family proteases during apoptosis.

The ICE/CED-3 family of proteases has been implicated in playing a fundamental role in programmed cell death. Bcl-2 protein represses a number of apoptotic death programs, but the biochemical mechanism of its action is not known. We investigated the activation of ICE/CED-3 proteases induced by three apoptotic stimuli (staurosporine, ceramide, and serum withdrawal) in the neuronal cell line GT1-7 and in cells overexpressing Bcl-2. Rapid activation of a 17 kDa subunit of an activated member of the ICE/CED-3 family is demonstrated by affinity-labeling GT1-7 extracts from apoptotic controls cells with a biotinylated ICE/CED-3 inhibitor. This activation corresponds to an increased ICE/CED-3-like protease activity in extracts measured by a fluorogenic substrate assay. In a cell-free system, these extracts induce apoptotic morphological changes in intact nuclei. All three activities are readily inhibited by treatment of control extracts with ICE/CED-3-like protease inhibitors. Overexpressed Bcl-2 inhibits the activation of the 17 kDa protein, the ICE/CED-3-like protease activity in the fluorogenic assay, and the induction of apoptotic morphological changes in HeLa nuclei in the cell-free system, similar to results obtained with ICE/CED-3 protease inhibitors. At the mRNA level, overexpression of Bcl-2 did not alter expression of five members of the ICE/CED-3 family: CPP32, ICE, Mch 2, Nedd 2, and TX. Overexpression of Bcl-2 prevented the apoptosis-induced processing of pro-Nedd 2 to the cleaved form. These data suggest that Bcl-2 participates upstream from the function of ICE/CED-3 proteases and may inhibit apoptosis by preventing the post-translational activation of ICE/CED-3 proteases.

Cleavage of actin by interleukin 1 beta-converting enzyme to reverse DNase I inhibition.

Three of the predominant features of apoptosis are internucleosomal DNA fragmentation, plasma membrane bleb formation, and retraction of cell processes. We demonstrate that actin is a substrate for the proapoptotic cysteine protease interleukin 1beta-converting enzyme. Actin cleaved by interleukin 1beta-converting enzyme can neither inhibit DNase I nor polymerize to its filamentous form as effectively as intact actin. These findings suggest a mechanism for the coordination of the proteolytic, endonucleolytic, and morphogenetic aspects of apoptosis.

Successful pregnancy outcome after cryopreservation of all fresh embryos with subsequent transfer into an unstimulated cycle.

OBJECTIVE: To assess the pregnancy outcome of freezing and storing all fresh embryos produced in a stimulated IVF cycle and replacing them in a subsequent nongonadotropin-stimulated cycle. DESIGN: Retrospective study. SETTING: University-associated assisted reproductive technology program. PATIENTS: We studied 36 patients (age range 23 to 44 years) who underwent cryopreservation of all fresh embryos in a controlled ovarian hyperstimulation (COH) cycle because of either the risk of severe ovarian hyperstimulation (24 patients, group 1) or the presence of an endometrial lining < 8 mm in thickness (12 patients, group 2). Five hundred fifty-five embryos were generated for replacement in 63 cycles. All embryos were cryopreserved in 1.5 M propanediol at the pronuclear or two-cell stage, and 264 embryos subsequently were transferred into a hormone replacement cycle (70%) or natural ovulatory cycle (30%). The average number of embryos transferred per patient was 4.2. RESULTS: Twenty-one clinical pregnancies were achieved, giving a pregnancy rate (PR) of 58.3% per patient (33.3% per cycle). The live birth rate was 50% per patient (28.6% per cycle). The implantation rate was 9.1%. Groups 1 and 2 had a similar PR per patient (58.3%). With 208 cryopreserved embryos remaining and considering the 33.3% PR per cycle, we expect the overall extrapolated PR to be 63.9%. CONCLUSIONS: This is the first series showing that freezing and storing all fresh embryos produced in a stimulated IVF cycle and replacing them in a subsequent nongonadotropin-stimulated cycle results in successful PRs. These results underlie the importance of a successful cryopreservation program in IVF and could be a possible approach to overcoming the alleged adverse effects of COH on the endometrium, thereby improving the chances of pregnancy when numerous embryos are obtained simultaneously.

Successful fertilization, pregnancy, and birth using epididymal sperm frozen 24 hours after conventional oocyte insemination.

OBJECTIVE: To assess if epididymal sperm cryopreserved 24 hours after exposure to oocytes in conventional IVF can be successfully used for intracytoplasmic sperm injection (ICSI) in a subsequent cycle. DESIGN: Case report. SETTING: University of California, Irvine, Center for Reproductive Health. PATIENTS: Two men with obstructive azoospermia requiring microsurgical epididymal sperm aspiration, IVF, and ICSI. INTERVENTIONS: Freezing of epididymal sperm 24 hours after egg exposure in conventional IVF and subsequent use for assisted fertilization in a new cycle. MAIN OUTCOME MEASURE: Frozen-thawed epididymal sperm survivability and maintenance of fertilization and pregnancy capacity. RESULTS: At the time of sperm aspiration procedure (cycle I) a total of 30 oocytes were available for insemination. Of these, 15 were used for conventional IVF resulting in 2 embryos (13%) and 15 were used for ICSI, resulting in 3 embryos (20%). Sperm was cryopreserved 24 hours after conventional IVF and thawed 6 months later in a new cycle. Upon thawing, sperm were still found to be motile and at this time (cycle II) only assisted fertilization was used. Of 27 oocytes injected, 12 (44%) produced normal, cleaving embryos. One singleton pregnancy with the birth of a healthy infant girl was achieved after the tubal transfer of 5 embryos. CONCLUSION: The birth of a normal, healthy infant girl with epididymal sperm frozen 24 hours after exposure to oocytes in conventional IVF emphasizes the value of freezing any aliquot of epididymal sperm, even if the motility is very low, to avoid additional surgery in the male. From a basic science standpoint, this observation may renew interest in the study of sperm cryopreservation after occurrence of acrosome reaction and hyperactivation.

Synthetic serum substitute (SSS): a globulin-enriched protein supplement for human embryo culture.

OBJECTIVE: The purpose of the present study was to evaluate whether an IVF protein supplement prepared from human serum albumin (HSA) and human globulins would retain performance characteristics equivalent to those reported for the commercial plasma expanders, Plasmatein (Alpha Therapeutics, Los Angeles, California) and Plasmanate (Cutter Biological, Miles Inc., Elkhart, Indiana). METHODS: Pronuclear-stage human embryos were randomly divided and cultured in human tubal fluid medium (HTF) supplemented with either HSA (5 mg/mL) or Plasmatein (10%, v/v; 5 mg/ml) as a means of indirectly assessing the effect alpha- and beta-globulins have on embryonic development. Those results coupled with the known composition characteristics of Plasmatein were used as the starting basis to formulate test lots of synthetic serum substitute (SSS). RESULTS: Significantly (P < 0.05) more of the human embryos cultured in Plasmatein supplemented medium reached the four-cell or greater stage by 40 hr postinsemination than a comparable group cultured in HSA alone. Lot 1 of SSS, formulated with HSA (84% of total protein) and human globulins (16% of total protein) and an aqueous lipoprotein fraction derived from human plasma (Excyte IV; Miles Diagnostics, Kankakee, Illinois), produced accelerated early embryonic growth relative to control murine embryos grown in the presence of Plasmatein, however, the percentage of the embryos reaching the hatched blastocyst stage was decreased (45 vs 100%). Human embryos from seven patients, randomized to HTF medium supplemented with Plasmatein or lot 1 of SSS, showed equivalent growth at 36-40 hr postinsemination. A microprecipitate developed in media supplemented with lot 1 after several days of culture. The Excyte IV concentration was reduced and, ultimately, eliminated from the subsequent and final prototype lots of SSS. Murine embryos grown in the presence of lipoprotein free SSS showed significantly accelerated (P < 0.01) growth at 17 hr postthaw compared to Plasmatein and all embryos progressed to hatching by 41 hr. Human embryos, randomized to either Plasmatein or lot 3 of SSS, showed significantly accelerated growth (P < 0.01) when scored at 38 hr following insemination. CONCLUSION: Synthetic serum substitute provides a convient, standardized means of adding protein to media used in assisted reproductive technology (ART) procedures.

The stages at which human fertilization arrests: microtubule and chromosome configurations in inseminated oocytes which failed to complete fertilization and development in humans.

The goal of fertilization is the union of one, and only one, sperm nucleus with the female pronucleus within the activated oocyte. For this to occur successfully, several events must transpire, including the incorporation of the entire spermatozoon into the oocyte, the completion of meiotic maturation with the extrusion of the second polar body, the metabolic activation of the previously quiescent oocyte, the decondensation of the sperm nucleus and the maternal chromosomes into the male and female pronuclei respectively, and the cytoplasmic migrations of the pronuclei, which bring them into apposition. Defects in any of these events are lethal to the zygote and might prove to be causes of infertility. In this study, the microtubules and DNA were imaged in inseminated human oocytes that had been discarded as unfertilized. The presence and number of incorporated sperm tails were also documented using a monoclonal antibody specific for the post-translationally modified acetylated-alpha-tubulin found in the tail, but not the oocyte, microtubules. An analysis of 211 oocytes from failed in-vitro fertilizations from 58 patient couples resulted in the determination of several previously undetectable phases at which fertilization arrests: (i) metaphase II arrest; (ii) arrest after the successful incorporation of the spermatozoon, (iii) arrest after the formation of the sperm aster; (iv) arrest during mitotic cell cycle progression; and (v) arrest during meiotic cell cycle progression. Data on polyspermy and arrested embryonic development are also presented. These results have implications for the diagnosis and treatment of female, as well as male, infertility.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of bcl-2 inhibits necrotic neural cell death.

Cell death has been described as either apoptotic, in which the cell actively participates, or necrotic, in which the cell is felt to be passive. The proto-oncogene bcl-2 has been shown to inhibit apoptosis in some hematopoietic and neural cells, by an unknown mechanism. We demonstrate that bcl-2 inhibits the necrosis of neural cells induced by glutathione depletion. This finding demonstrates that bcl-2 does not inhibit the cellular death program directly; rather, bcl-2 modulates a cellular process that leads to apoptosis under some conditions but necrosis under others.