Decrease In Body Size Research Articles

Polyploidy, body size, and opportunities for genetic enhancement and fixation of heterozygosity in plants

Polyploidy, the presence of more than two chromosome sets, is rare in animals, but is wide spread in plants. Polyploidy is believed to play an important role in speciation and diversification of plants. It is conjectured that almost all angiosperms are likely to be ancient polyploids i.e. palaeopolyploids that have undergone diploidization through differential mutation, elimination and inversion of duplicated chromosomes. Therefore, understanding of consequences of gene duplication on functional divergence, developmental behavior and genome stability is of utmost importance from utilitarian view point. Studies conducted by our group for over a quarter century on the cyotogenetics of polyploids on an array of medicinal and aromatic plants have enabled us to develop strategies to realize high fertility in the autotetraploids. It is surmised that pre-selection of diploid progenitor with low chiasmate association, preferably with distal chiasma localization facilitates high bivalent pairing and balanced meiotic segregation in the derived autotetraploid, and thereby promising high fertility. This has implications in ploidy mediated fixation of heterozygosity and genetic enhancement. However, the elevated ploidy level does not always bring about increase in body size. Both, increase or decrease in body size happen to occur consequent to genomic duplication, depending upon the species and composition of native secondary metabolites / cost of metabolic load. Of course, polyploidization does bring about increase in secondary metabolite concentration and DNA methylation. Further, the patterns of chromosome / ploidy variation encountered in callus cultures over passage of subcultures are indicative of variation happening over evolutionary timescale. The details concerning such issues are dealt in this article based on our own experimental observations and are discussed from utilitarian view point for further researches.

Sciatic nerve regeneration is not inhibited by anti-NGF antibody treatment in the adult rat

Elevated nerve growth factor (NGF) is believed to play a role in many types of pain. An NGF-blocking antibody (muMab 911) has been shown to reduce pain and hyperalgesia in pain models, suggesting a novel therapeutic approach for pain management. Since NGF also plays important roles in peripheral nervous system development and sensory nerve outgrowth, we asked whether anti-NGF antibodies would adversely impact peripheral nerve regeneration. Adult rats underwent a unilateral sciatic nerve crush to transect axons and were subcutaneously dosed weekly for 8weeks with muMab 911 or vehicle beginning 1day prior to injury. Plasma levels of muMab 911 were assessed from blood samples and foot print analysis was used to assess functional recovery. At 8-weeks post-nerve injury, sciatic nerves were prepared for light and electron microscopy. In a separate group, Fluro-Gold was injected subcutaneously at the ankle prior to perfusion, and counts and sizes of retrogradely labeled and unlabeled dorsal root ganglion neurons were obtained. There was no difference in the time course of gait recovery in antibody-treated and vehicle-treated animals. The number of myelinated and nonmyelinated axons was the same in the muMab 911-treated crushed nerves and intact nerves, consistent with observed complete recovery. Treatment with muMab 911 did however result in a small decrease in average cell body size on both the intact and injured sides. These results indicate that muMab 911 did not impair functional recovery or nerve regeneration after nerve injury in adult rats.

Fecundity and sexual size dimorphism of wolf spiders (Araneae: Lycosidae) along an elevational gradient in the Arctic

Fecundity and body size are central fitness- related traits, and their intra-specific responses to envi- ronmental variation are receiving increasing attention in the context of climate change. Recent results from Greenland indicate that temporal and spatial variation in body size differences between sexes (sexual size dimor- phism) may be widespread among wolf spider species and could be related to climate. Here, we tested whether vari- ation in elevation affected body size of three wolf spider (Araneae: Lycosidae) species in low-Arctic Canada, whe- ther the sexes differed in their response to the cline, and whether changes in local density influenced this relationship. We also tested whether fecundity changed with elevation in two of the species, independent of body size variation. We found a significant sex-elevation inter- action for Pardosa lapponica: female size decreased more in response to elevation than that of males. Males and females of Pardosa uintana decreased significantly in size with elevation at a similar rate. Alopecosa aculeata males increased in body size along the gradient while females did not. Pardosa lapponica females, but not P. uintana females, showed significant reduction in fecundity in response to elevation. P. uintana showed significant decreases in body size with increases in its population density. Changes in temperature and potential resource availability along the elevational gradient are probably causing these species- and sex-specific responses. Further summer warming of the region may alleviate current con- straints on growth and reproduction of these species although sex-specific responses may affect their population dynamics.

Mutation of the Diamond-Blackfan Anemia Gene Rps7 in Mouse Results in Morphological and Neuroanatomical Phenotypes

The ribosome is an evolutionarily conserved organelle essential for cellular function. Ribosome construction requires assembly of approximately 80 different ribosomal proteins (RPs) and four different species of rRNA. As RPs co-assemble into one multi-subunit complex, mutation of the genes that encode RPs might be expected to give rise to phenocopies, in which the same phenotype is associated with loss-of-function of each individual gene. However, a more complex picture is emerging in which, in addition to a group of shared phenotypes, diverse RP gene-specific phenotypes are observed. Here we report the first two mouse mutations (Rps7Mtu and Rps7Zma) of ribosomal protein S7 (Rps7), a gene that has been implicated in Diamond-Blackfan anemia. Rps7 disruption results in decreased body size, abnormal skeletal morphology, mid-ventral white spotting, and eye malformations. These phenotypes are reported in other murine RP mutants and, as demonstrated for some other RP mutations, are ameliorated by Trp53 deficiency. Interestingly, Rps7 mutants have additional overt malformations of the developing central nervous system and deficits in working memory, phenotypes that are not reported in murine or human RP gene mutants. Conversely, Rps7 mouse mutants show no anemia or hyperpigmentation, phenotypes associated with mutation of human RPS7 and other murine RPs, respectively. We provide two novel RP mouse models and expand the repertoire of potential phenotypes that should be examined in RP mutants to further explore the concept of RP gene-specific phenotypes.

Phytoplankton Cell Size: Intra- and Interspecific Effects of Warming and Grazing

Decreasing body size has been suggested as the third universal biological response to global warming after latitudinal/altitudinal range shifts and shifts in phenology. Size shifts in a community can be the composite result of intraspecific size shifts and of shifts between differently sized species. Metabolic explanations for the size shifts dominate in the literature but top down effects, i.e. intensified size-selective consumption at higher temperatures, have been proposed as alternative explanation. Therefore, we performed phytoplankton experiments with a factorial combination of warming and consumer type (protist feeding mainly on small algae vs. copepods mainly feeding on large algae). Natural phytoplankton was exposed to 3 (1st experiment) or 4 (2nd experiment) temperature levels and 3 (1st experiment: nano-, microzooplankton, copepods) or 2 (2nd experiment: microzooplankton, copepods) types of consumers. Size shifts of individual phytoplankton species and community mean size were analyzed. Both, mean cell size of most of the individual species and mean community cell size decreased with temperature under all grazing regimes. Grazing by copepods caused an additional reduction in cell size. Our results reject the hypothesis, that intensified size selective consumption at higher temperature would be the dominant explanation of decreasing body size. In this case, the size reduction would have taken place only in the copepod treatments but not in the treatments with protist grazing (nano- and microzooplankton).

Effects of host plant and maternal feeding experience on population vital rates of a specialized leaf beetle

In herbivorous insects, the interaction between adult preference and progeny performance on specific host plants is modified by maternal feeding experience and host plant quality. Ultimately, changes in the strength of this interaction can affect insect population dynamics. In this study, we hypothesized that adult host plant preference influences progeny performance through a maternal feeding experience × host plant interaction, that is, the effect of adult feeding experience on progeny performance will depend on the host plant. Second, that decoupling of the preference–performance relationship due to host switching results in different population vital rates changing population dynamics. An increase in development time and a decrease in body size of individuals in the alternate host should decrease population growth. We tested these hypotheses using two lines of the tortoise beetle Chelymorpha varians Blanchard fed with two hosts (Convolvulus arvensis and Calystegia sepium). Maternal feeding experience treatments were crossed with host plant species, and the offspring’s developing time and adult size were measured. The host plant influence on the beetle’s population vital rates was tested using stage-structured matrix population models and life table response experiments. Host plant preference affected offspring body size through a host plant effect that contributed to adaptive life history responses only in the better quality host. C. varians’ population growth was positive when fed with either host; comparatively, however, C. sepium had a negative effect on growth by reducing all transition probabilities of the life cycle stages of the beetle. Here, we show that individuals of C. varians prefer and perform differently on distinct hosts and that these patterns influence population vital rates in different ways. When beetles prefer the host plant where their progeny performs best, life history responses and life stage transitions lead to higher population growth; otherwise, growth rate decreases.

Allometry of sexual size dimorphism in domestic dog.

BackgroundThe tendency for male-larger sexual size dimorphism (SSD) to scale with body size – a pattern termed Rensch's rule – has been empirically supported in many animal lineages. Nevertheless, its theoretical elucidation is a subject of debate. Here, we exploited the extreme morphological variability of domestic dog (Canis familiaris) to gain insights into evolutionary causes of this rule.Methodology/Principal FindingsWe studied SSD and its allometry among 74 breeds ranging in height from less than 19 cm in Chihuahua to about 84 cm in Irish wolfhound. In total, the dataset included 6,221 individuals. We demonstrate that most dog breeds are male-larger, and SSD in large breeds is comparable to SSD of their wolf ancestor. Among breeds, SSD becomes smaller with decreasing body size. The smallest breeds are nearly monomorphic.Conclusions/SignificanceSSD among dog breeds follows the pattern consistent with Rensch's rule. The variability of body size and corresponding changes in SSD among breeds of a domestic animal shaped by artificial selection can help to better understand processes leading to emergence of Rensch's rule.

Northward range extension of a diminutive-sized mammal (Ectocion parvus) and the implication of body size change during the Paleocene–Eocene Thermal Maximum

An abrupt global warming event marks the Paleocene–Eocene boundary, known as the Paleocene–Eocene Thermal Maximum (PETM). The event is distinguished in the strata globally by a significant negative excursion of δ13C ratio values. The response of the terrestrial biota to the abrupt climatic change has been well studied in northern Wyoming in the Bighorn Basin, where it has been observed that the mammalian fauna during the global warming event is represented by smaller, but morphologically similar species to those found later in the Eocene. Various hypotheses have been proposed to explain the observation smaller body sizes during the global warming event. In this article, evidence is presented to support the hypothesis that the observed body size decrease during the PETM was influenced by the appearance of smaller southern species who extended their geographic range northward during the abnormal global warming event. Using disperse organic carbon isotopic ratios of bulk sediment, the negative excursion of δ13C was located in the Piceance Creek Basin of western Colorado, 400km to the south of the Bighorn Basin. Below the stratigraphic level marking the negative carbon excursion in the Piceance Creek Basin are five specimens of the phenacodontid mammal (Ectocion parvus), a diminutive species of the genus Ectocion restricted to the basal Eocene (Wa-0 Biozone) in northern Wyoming. The five specimens of E. parvus are associated with a late Paleocene (Clarkforkian) mammalian fauna in Colorado, implying that the diminutive species extended its geographic range northward during the global warming event. This evidence supports biogeographic models that assume poleward biogeographic shifts during global warming events, and will have modern day implications for the conservation of species as global temperatures rise in the near future.

Arginine exposure alters ectonucleotidase activities and morphology of zebrafish larvae (Danio rerio)

Hyperargininemia is an inborn error of metabolism (IEM) characterized by tissue accumulation of arginine (Arg). Mental retardation and other neurological features are common symptoms in hyperargininemic patients. Considering purinergic signaling has a crucial role from the early stages of development and underlying mechanisms of this disease are poorly established, we investigated the effect of Arg administration on locomotor activity, morphological alterations, and extracellular nucleotide hydrolysis in larvae and adult zebrafish. We showed that 0.1mM Arg was unable to promote changes in locomotor activity. In addition, 7-day-post-fertilization (dpf) larvae treated with Arg demonstrated a decreased body size. Arg exposure (0.1mM) promoted an increase in ATP, ADP, and AMP hydrolysis when compared to control group. These findings demonstrated that Arg might affect morphological parameters and ectonucleotidase activities in zebrafish larvae, suggesting that purinergic system is a target for neurotoxic effects induced by Arg.

Positive Regulation by γ-Aminobutyric Acid B Receptor Subunit-1 of Chondrogenesis through Acceleration of Nuclear Translocation of Activating Transcription Factor-4

A view that signaling machineries for the neurotransmitter γ-aminobutyric acid (GABA) are functionally expressed by cells outside the central nervous system is now prevailing. In this study, we attempted to demonstrate functional expression of GABAergic signaling molecules by chondrocytes. In cultured murine costal chondrocytes, mRNA was constitutively expressed for metabotropic GABA(B) receptor subunit-1 (GABA(B)R1), but not for GABA(B)R2. Immunohistochemical analysis revealed the predominant expression of GABA(B)R1 by prehypertrophic to hypertrophic chondrocytes in tibial sections of newborn mice. The GABA(B)R agonist baclofen failed to significantly affect chondrocytic differentiation determined by Alcian blue staining and alkaline phosphatase activity in cultured chondrocytes, whereas newborn mice knocked out of GABA(B)R1 (KO) showed a decreased body size and delayed calcification in hyoid bone and forelimb and hindlimb digits. Delayed calcification was also seen in cultured metatarsals from KO mice with a marked reduction of Indian hedgehog gene (Ihh) expression. Introduction of GABA(B)R1 led to synergistic promotion of the transcriptional activity of activating transcription factor-4 (ATF4) essential for normal chondrogenesis, in addition to facilitating ATF4-dependent Ihh promoter activation. Although immunoreactive ATF4 was negligibly detected in the nucleus of chondrocytes from KO mice, ATF4 expression was again seen in the nucleus and cytoplasm after the retroviral introduction of GABA(B)R1 into cultured chondrocytes from KO mice. In nuclear extracts of KO chondrocytes, a marked decrease was seen in ATF4 DNA binding. These results suggest that GABA(B)R1 positively regulates chondrogenesis through a mechanism relevant to the acceleration of nuclear translocation of ATF4 for Ihh expression in chondrocytes.

Communicating Stigma About Body Size

Body-size stigma is a well-documented phenomenon, particularly for large bodies (Puhl & Brownell, 2003), but few studies have investigated the features of body-related stigma communication. This article uses Smith's (2007a) stigma communication framework to analyze descriptions of male and female bodies of various sizes for their stigma content. Analyses reveal that elements of stigma communication appeared in 46.5% of comments across all bodies. The most common elements of stigma communication were severe labeling and negative comparison to body ideals. The most stigmatized body was the large male body; the second most stigmatized body was the very small female body. This article shows that stigmatizing communication occurs across the spectrum of body sizes for both genders. The implications of weight-based stigma communication on emotional and physical health are discussed. Implications for future health communication interventions aimed at decreasing body size stigma are presented.

Mating, ovariole number and sperm production of the dengue vector mosquito Aedes aegypti (L.) in Australia: broad thermal optima provide the capacity for survival in a changing climate

Little is known about mating, ovariole number and sperm production of Aedes aegypti (L.) in Australia, especially in relation to climate. To determine the extent of interpopulation variation and thermal dependence of reproductive traits in A. aegypti, laboratory studies are conducted using colonies originating from up to four locations in Queensland, Australia. Observations of insemination reveal that these behaviours are temperature‐dependent, although humidity levels appear to have little effect, with only small increases in insemination at higher humidities. No noteworthy variations in thermal optima (temperature ranges within which maximal performance occurs) for such behaviours are observed between colonies, with all showing high levels of insemination between 25 and 35 °C. Both male and female maximum fecundity for A. aegypti are also found to be temperature‐dependent. Sperm counts, not hitherto obtained for Australian A. aegypti, range from approximately 3000–5000 per male, with counts increasing with increased rearing and holding temperature, despite a decreasing body size. Conversely, ovary size decreases with temperature and body size, from approximately 100 ovarioles per female at 17 °C, to 85 at 35 °C. The lack of variation in reproductive capacity between colonies of different geographical origin indicates that any locally‐acting selective pressures are not driving divergence in key reproductive traits such as insemination ability and fecundity. This may be because the source populations used are not from sufficiently diverse climates. Nonetheless, the broad thermal optima for reproductive traits in A. aegypti are suggestive of limitations on these traits not being responsible for limiting distribution and population growth in the event of projected mean temperature rises.

Age and body size of Salamandrella keyserlingii (Caudata: Hynobiidae): a difference in altitudes, latitudes, and temperatures

The debate surrounding Bergmann’s rule, in which the body size of animals is predicted to be larger in cooler environments, is still open concerning ectotherms. Our goal was to test this rule in the broadest ranging amphibian species Salamandrella keyserlingii. We determined age and body size in a cooler region (Darhadyn, Mongolia: mean yearly air temperature = –8.31 °C) using skeletochronology, and compared their differences in altitude, latitude, and temperature with those of a warmer area (Kushiro, Japan: 7.98 °C). In Darhadyn, both sexes reached sexual maturity at 5–6 years of age (growth coefficient: male = 0.585, female = 0.266), 2–3 years later than those in Kushiro (male = 1.341, female = 1.129). Mean body size was smaller in Darhadyn (53.08 mm) than in Kushiro (57.63 mm) for males despite their constant metamorphic size around 30 mm. We also analyzed data available from published studies for 27 populations within the geographic range of this species from 43 to 69°N across a 2,900-km long latitudinal gradient. The analysis indicated an intraspecific tendency to decrease body size with increased latitude from 43 to 57°N, to increase size from 57 to 69°N, and to decrease body size with decreased temperature from 8 to –7 °C and increase size from –7 to –15 °C. This pattern does not follow the intraspecific extension of Bergmann’s rule and may follow the converse of Terentjev’s optimum rule—a rule formulated to be an inverted-U shaped curve between increased latitude (or decreased temperature) and increased body size.

Environment-dependent regime of longevity selection in the chromosomally polymorphic species Leptysma argentina (Acrididae: Orthoptera)

In previous papers it was reported that a Robertsonian translocation (centric fusion) affected external phenotype in the grasshopper Leptysma argentina and that thorax height was the target of adult viability selection. In the present paper two populations of L. argentina at different latitudes, with different centric fusion frequencies, were studied. It was demonstrated that selection acts on roughly the same targets but in opposite directions. In the northernmost population longevity selection acted primarily on thorax height (TH), leading to an increase of that variable. In the southern population, longevity selection leads to an increased femur length (FL) but to a decreased body size (including TH). Longevity selection affects karyotype frequency, leading to an increase of fusion homozygote frequency; however, fusion 3/6 significantly increases FL. This is consistent with an increase in fusion frequency along the season. The fact that longevity selection in one population increases and in another dec...

Abstract 1302: Effect of intestinal-specific Kaiso overexpression on the APC MIN/+ mouse colon cancer model

Abstract The canonical Wnt signaling pathway is a crucial regulator of various cellular processes during embryogenesis but when aberrantly activated, it leads to tumorigenesis. The key downstream effector of the Wnt pathway is the Armadillo protein, β-catenin, which was first characterized as a cytoplasmic cofactor for the transmembrane, cell-cell adhesion tumor suppressor, E-cadherin. Recent evidence from our lab and others indicates that another E-cadherin cofactor, p120ctn and its binding partner, the POZ-ZF transcription factor Kaiso, co-regulate a subset of Wnt/β-catenin target genes and antagonize Wnt signaling. Specifically, using a Xenopus model system, we and others found that Kaiso overexpression rescued the β-catenin-induced duplicate axis phenotype; this implicated Kaiso as a negative regulator of Wnt signaling. However, it remains to be determined whether an analogous antagonistic role for Kaiso is conserved in mammals. Indeed, when Kaiso-null mice (which were viable and had no overt developmental defects or tumors) were crossed with the APCMIN/+ mouse model of colon cancer, the progeny had delayed tumor onset and reduced polyp size. This suggested that Kaiso played a positive role in tumor initiation and possibly cell proliferation in mammals. To resolve this discrepancy, we generated intestine-specific Kaiso overexpressing transgenic mice (KaisoTg/+) for subsequent mating with the APCMIN/+ mouse model of colon cancer. Histological analysis of small and large intestines from KaisoTg/+ and non-Tg mice revealed no gross morphological differences. Immunohistochemical (IHC) and immunofluorescence (IF) staining revealed strong nuclear Kaiso staining in intestinal tissues from KaisoTg/+ mice whereas intestinal tissues from non-Tg mice displayed weak cytoplasmic or no Kaiso staining. We detected no difference in β-Catenin expression levels in tissues from KaisoTg/+ mice and their wildtype littermates. This suggests that Kaiso's regulation of WNT signaling is downstream of its main effector β-Catenin. KaisoTg-APCMIN/+ double mutant mice have been generated and surprisingly they display decreased body size and weight, and have a decreased life span when compared to the parentals (i.e. KaisoTg or APCMIN/+). Current studies are aimed at assessing polyp formation and elucidating the expression levels of p120ctn, β-catenin, E-cadherin and cyclinD1 in the KaisoTg-APCMIN/+ intestines. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1302. doi:1538-7445.AM2012-1302

Morphometric and genetic differentiation of two sibling gossamer-wing damselflies, Euphaea formosa and E. yayeyamana, and adaptive trait divergence in subtropical East Asian islands.

Insular species frequently demonstrate different tendencies to become smaller or larger than their continental relatives. Two sibling gossamer—wing damselflies, Euphaea formosa (Odonata: Euphaeidae) from Taiwan and E. yayeyamana from the Yaeyama Islands of Japan, have no clear structural differentiation, and can only be recognized by their geographical distribution, sizes, and subtle differences in wing shape and coloration. This study combined morphometric and genetic techniques to investigate the adaptive significance of trait divergence and species status in these two Euphaea damselflies. Phylogenetic analyses of the mitochondrial cox2 sequences demonstrated that the two damselflies are monophyletic lineages and constitute valid phylogenetic species. The landmark—based geometric morphometrics indicated that the two damselflies are different morphological species characterized by distinctive wing shapes. The larger E. formosa exhibited broader hind wings, whereas E. yayeyamana had narrower and elongated forewings. The body size and wing shape variations among populations of the two species do not follow the expected pattern of neutral evolution, suggesting that the evolutionary divergence of these two traits is likely to be subjected to natural or sexual selection. The decreased body size, elongated forewings, and narrower hind wings of E. yayeyamana may represent insular adaptation to limited resources and reduced territorial competition on smaller islands.

Ant attendance reduces flight muscle and wing size in the aphid Tuberculatus quercicola

In otherwise mutualistic relationships between aphids and ants, attendance by ants often has negative impacts on aphids. For example, in a previous study using traps in the field, the aphid Tuberculatus quercicola, which exhibits mutualistic interactions with ants, showed extremely low dispersal rates, despite having long wings. This study investigates whether components of the flight apparatus (mesonotum length, flight muscle and wings) differ between aphids attended by ants and not attended by ants. Randomized block analysis of variance, using body length as a covariate, showed that ant attendance has a negative influence on aphid flight apparatus. This result indicates that aphids produce honeydew at the expense of resource investment in flight apparatus. Since the dispersal of T. quercicola is limited under ant attendance, the reduction in flight apparatus could precede a decrease in body size. This study also showed that flight apparatus was more developed in aphids under ant-exclusion conditions. This may imply that T. quercicola fly when ants are not available. The maintenance of flight apparatus in T. quercicola might therefore be partly explained by gene flow on the rare occasions that this aphid species disperses.

Size increase in high elevation ground squirrels over the last century

AbstractThere is increasing evidence for morphological change in response to recent environmental change, but how this relates to fluctuations in geographic range remains unclear. We measured museum specimens from two time periods (1902–1950 and 2000–2008) that vary significantly in climate to assess if and how two high elevation contracting species of ground squirrels in the Sierra Nevada of California, Belding's ground squirrel (Urocitellus beldingi) and the golden‐mantled ground squirrel (Callospermophilus lateralis), and one lower elevation, stable species, the California ground squirrel (Otospermophilus beecheyi), have responded morphologically to changes over the last century. We measured skull length (condylobasal length), an ontogenetically more labile trait highly correlated with body size, and maxillary toothrow length, a more developmentally constrained trait predictive of skull shape. C. lateralis and U. beldingi, both obligate hibernators, have increased in body size, but have not changed in shape. In contrast, O. beecheyi, which only hibernates in parts of its range, has shown no significant change in either morphometric trait. The increase in body size in the higher elevation species, hypothesized to be a plastic effect due to a longer growing season and thus prolonged food availability, opposes the expected direction of selection for decreased body size under chronic warming. Our study supports that population contraction is related to physiological rather than nutritional constraints.

Life history change in response to fishing and an introduced predator in the East African cyprinid Rastrineobola argentea

Fishing and introduced species are among the most important stressors affecting freshwaters and can also be strong selective agents. We examined the combined effects of commercial fishing and an introduced predator (Nile perch, Lates niloticus) on life history traits in an African cyprinid fish (Rastrineobola argentea) native to the Lake Victoria basin in East Africa. To understand whether these two stressors have driven shifts in life history traits of R. argentea, we tested for associations between life history phenotypes and the presence/absence of stressors both spatially (across 10 Ugandan lakes) and temporally (over four decades in Lake Victoria). Overall, introduced Nile perch and fishing tended to be associated with a suite of life history responses in R. argentea, including: decreased body size, maturation at smaller sizes, and increased reproductive effort (larger eggs; and higher relative fecundity, clutch volume, and ovary weight). This is one of the first well-documented examples of fisheries-induced phenotypic change in a tropical, freshwater stock; the magnitude of which raises some concerns for the long-term sustainability of this fishery, now the most important (by mass) in Lake Victoria.

Evolution of the Earliest Horses Driven by Climate Change in the Paleocene-Eocene Thermal Maximum

Body size plays a critical role in mammalian ecology and physiology. Previous research has shown that many mammals became smaller during the Paleocene-Eocene Thermal Maximum (PETM), but the timing and magnitude of that change relative to climate change have been unclear. A high-resolution record of continental climate and equid body size change shows a directional size decrease of ~30% over the first ~130,000 years of the PETM, followed by a ~76% increase in the recovery phase of the PETM. These size changes are negatively correlated with temperature inferred from oxygen isotopes in mammal teeth and were probably driven by shifts in temperature and possibly high atmospheric CO(2) concentrations. These findings could be important for understanding mammalian evolutionary responses to future global warming.