Evolutionary divergence in life history traits among populations of the Lake Malawi cichlid fish Astatotilapia calliptera

During the early stages of adaptive radiation, populations diverge in life history traits such as egg size and growth rates, in addition to eco‐morphological and behavioral characteristics. However, there are few studies of life history divergence within ongoing adaptive radiations. Here, we studied Astatotilapia calliptera, a maternal mouthbrooding cichlid fish within the Lake Malawi haplochromine radiation. This species occupies a rich diversity of habitats, including the main body of Lake Malawi, as well as peripheral rivers and shallow lakes. We used common garden experiments to test for life history divergence among populations, focussing on clutch size, duration of incubation, egg mass, offspring size, and growth rates. In a first experiment, we found significant differences among populations in average clutch size and egg mass, and larger clutches were associated with smaller eggs. In a second experiment, we found significant differences among populations in brood size, duration of incubation, juvenile length when released, and growth rates. Larger broods were associated with smaller juveniles when released and shorter incubation times. Although juvenile growth rates differed between populations, these were not strongly related to initial size on release. Overall, differences in life history characters among populations were not predicted by major habitat classifications (Lake Malawi or peripheral habitats) or population genetic divergence (microsatellite‐based F_ST). We suggest that the observed patterns are consistent with local selective forces driving the observed patterns of trait divergence. The results provide strong evidence of evolutionary divergence and covariance of life history traits among populations within a radiating cichlid species, highlighting opportunities for further work to identify the processes driving the observed divergence.     

Quantitative genetic analysis of larval life history traits in two alpine populations of Rana temporaria

We estimated genetic and maternal variance components of larval life history characters in alpine populations of Rana temporaria (the common frog) using a full-sib/half-sib breeding design. We studied trait plasticity by raising tadpoles at 14 or 20°C in the laboratory. Larval period and metamorphic mass were greater at 14°C. Larval period did not differ between populations, but high elevation metamorphs were larger than low elevation metamorphs. Significant additive variation for larval period was detected in the low altitude population. No significant additive variation was detected for mass at metamorphosis (MM), which instead displayed significant maternal effects. Plasticity in metamorphic mass of froglets was greater in the high altitude population. The plastic response of larval period to temperature did not differ between the populations. Evolution of metamorphic mass is likely constrained by lack of additive genetic variation. In contrast, significant heritability for larval period suggests this trait may evolve in response to environmental change. These results differ from other studies on R. temporaria, suggesting that populations of this broadly distributed species present substantial geographic variation in the genetic architecture and plasticity of tadpole life history traits.     

The role of life history traits in mammalian invasion success

Why some organisms become invasive when introduced into novel regions while others fail to even establish is a fundamental question in ecology. Barriers to success are expected to filter species at each stage along the invasion pathway. No study to date, however, has investigated how species traits associate with success from introduction to spread at a large spatial scale in any group. Using the largest data set of mammalian introductions at the global scale and recently developed phylogenetic comparative methods, we show that human‐mediated introductions considerably bias which species have the opportunity to become invasive, as highly productive mammals with longer reproductive lifespans are far more likely to be introduced. Subsequently, greater reproductive output and higher introduction effort are associated with success at both the establishment and spread stages. High productivity thus supports population growth and invasion success, with barriers at each invasion stage filtering species with progressively greater fecundity.     

The combined effects of hypoxia and fish kairomones on several physiological and life history traits of Daphnia

1. Numerous studies have tested the combined effect of the threat of predation by fish and low oxygen concentrations on the phenotypic plasticity of Daphnia. These studies assessed the trade‐off between minimising predation risk and the negative effects of oxygen deficiencies in the context of depth selection behaviour. We tested whether this trade‐off also affects physiological and life history traits. We expected an interactive effect between the threat of fish predation and low oxygen concentrations, such, that the net effect of both stressors would be antagonistic (lower than the sum of each of the stressors acting separately), rather than additive (or synergistic) on the majority of traits investigated, but we predicted synergistic effects on heat shock proteins (HSPs).
2. To test this, we performed life table experiments in different oxygen concentrations (normoxia and hypoxia) and levels of predation threat (the presence and absence of fish kairomones) on HSP70 and putative HSP110, haemoglobin concentration and life history traits with small‐bodied Daphnia galeata and large‐bodied Daphnia pulex originating from waterbodies where there were different risks of fish predation.
3. As predicted, the net effect of both stressors was antagonistic for most of the physiological and ecological variables studied. The presence of kairomones resulted in decreased body size of adults, egg size, egg size in relation to brood chamber volume, and in increased clutch size in relation to body size. These effects were weaker in hypoxia than in normoxia, which may suggest an existence of adaptive responses caused by a lower perceived risk in hypoxia than in normoxia, as the foraging abilities of fish are limited by oxygen deficiencies.
4. The presence of kairomones hampered the production of haemoglobin in hypoxia for the clones of larger‐bodied species, which suggests the existence of a trade‐off between reduced visibility under positive‐size selective predation risk and increased efficiency of oxygen transport to body tissues. The presence of kairomones and hypoxia resulted in an increased level of putative HSP110, and the effect of kairomones was stronger in hypoxia than in normoxia. More complex results were obtained for the effect of both stressors on the level of HSP70.
5. The findings of our study provide a new insight on the interactions between planktivorous fish and zooplankton in aquatic food webs. More specifically, these findings suggest the existence of unexplored size‐dependent eco‐physiological trade‐offs between minimising predation risk and mitigating the negative effects of oxygen deficiencies.

     

Isotopic change throughout the life history of a Lake Malawi cichlid fish

Clear changes in body size-isotope (carbon and nitrogen) trajectories of Pseudotropheus callainos , a cichlid belonging to the endemic haplochromine species radiation in Lake Malawi, were found that corresponded with an ontogenetic dietary shift from predominantly planktonic to benthic food sources. The results indicated that dietary switching was a proximate cause of isotopic change over the life history of this species and confirmed the value of stable isotope signatures for inferring diet. The data also illustrated that possible variability of signatures over the life history of a species should be considered when using stable isotope ratios to investigate fine-scale ecological differentiation among taxa.     

Host-related life history traits in interspecific hybrids of cactophilic Drosophila

In the genus Drosophila (Diptera: Drosophilidae), interspecific hybridization is a rare phenomenon. However, recent evidence suggests a certain degree of introgression between the cactophilic siblings Drosophila buzzatii Patterson & Wheeler and Drosophila koepferae Fontdevila & Wasserman. In this article, we analyzed larval viability and developmental time of hybrids between males of D. buzzatii and females of D. koepferae, raised in media prepared with fermenting tissues of natural host plants that these species utilize in nature as breeding sites. In all cases, developmental time and larval viability in hybrids was not significantly different from parental lines and, depending on the cross, hybrids developed faster than both parental species or than the slowest species. When data of wing length were included in a discriminant function analysis, we observed that both species can be clearly differentiated, while hybrids fell in two categories, one intermediate between parental species and the other consisting of extreme phenotypes. Thus, our results point out that hybrid fitness, as measured by developmental time and viability, is not lower than in the parental species.     

Temporal variation and its drivers in the elemental traits of four boreal plant species

4种北方植物元素性状的时间变化及其驱动因素 植物种内性状的变异对个体适合度和草食动物的觅食有重要影响。对于植物来说,在空间维度上的性状变异已经得到了很好的证明。然而,对性状变异的时间维度仍知之甚少,但其可能受生长度日、温度和降水季节差异的影响。本研究的目的是量化4种常见的北方植物物种性状的种内时间变异及其变异的驱动因素。我们对4种常见树种的叶片进行了为期两年的元素和化学计量性状采样(%C, %N, %P, C:N, C:P, N:P)。本研究分两个步骤进行,首先将广义线性模型(GzLM, n = 24)与我们研究的物种的元素和化学计量性状拟合,以测试它们是否随年份而变化。当我们获得时间变异性的证据时,我们拟合第二组GzLMs (n = 8),将温度、生产力和湿度作为解释变量。研究结果显示,除了两个例外,4种北方植物的大部分元素和化学计量性状都没有时间变异性。年份是所有4种植物的碳百分比(R² = 0.47–0.67)以及香脂冷杉(Abies balsamea)中多种元素和化学计量性状(5/8, R² = 0.29–0.67)的重要预测因子。因此,碳百分比的变化与年际差异有关,而与限制北方森林养分的氮和磷关系更大。这些研究结果还表明,由于生活史的差异,针叶树的化学计量比落叶植物的化学计量的年际差异更大。生长度日是第二轮模型中最频繁出现的变量(8/8 次,R² = 0.21–0.41),表明温度是这些性状时间变异的重要驱动因素。     

Reaction norms of life history traits in response to zinc in Thlaspi caerulescens from metalliferous and nonmetalliferous sites

* We examined phenotypic plasticity of fitness components in response to zinc (Zn) in the Zn hyperaccumulator, Thlaspi caerulescens. * Two populations from Zn-enriched soils (M) and two populations from normal soils (NM) were grown in pots at three Zn concentrations (0, 1000 and 8000 mg kg(-1) Zn), for an entire life cycle. Growth, Zn accumulation and fitness components were assessed. * Based on vegetative growth, M and NM populations had similar Zn tolerance at 1000 mg kg(-1) Zn. However, reproductive output was markedly decreased in NM at 1000 and 8000 mg kg(-1) Zn. In M populations, Zn did not affect fitness. However, low Zn status enhanced reproductive output in year 1 compared with year 2 and decreased survival after the first flowering season. * M populations are able to achieve equal fitness across a broad range of Zn concentrations in soil by different combinations of fecundity and longevity. No cost of higher tolerance was demonstrated in M populations. Reproductive traits appeared to be a more sensitive indicator of tolerance than vegetative growth.     

Resolution of the early life history of a reef fish using otolith chemistry

We used the elemental signatures in otoliths of the damselfish Pomacentrus coelestis as a proxy for conditions experienced prior to settlement. Fish from the southern Great Barrier Reef (GBR) differed in their pre-settlement otolith chemistry, indicating that they had occupied different water masses during their pelagic stage, thus suggesting multiple larval sources. Fish from reefs in the northern GBR did not differ greatly in their pre-settlement otolith chemistry, suggesting a single larval source. Using near-natal signatures, we determined that ~67% of these signatures matched the signature established for Lizard Island (LZ), suggesting LZ could be a source reef. However, these results could also be the result of poor separation among reefs caused by reefs sharing water masses. Otolith chemistry also revealed that 50–70% of all fish examined settled on the reef the day they encountered it, while some fish spent up to 4 days near the reef prior to settlement.     

Photoperiod and variation in life history traits in core and peripheral populations in the damselfly Lestes sponsa

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Effects of four generations of density-dependent selection on life history traits and their plasticity in a clonally propagated plant

Life history evolution of many clonal plants takes place with long periods of exclusively clonal reproduction and under largely varying ramet densities resulting from clonal reproduction. We asked whether life history traits of the clonal herb Ranunculus reptans respond to density-dependent selection, and whether plasticity in these traits is adaptive. After four generations of exclusively clonal propagation of 16 low and 16 high ramet-density lines, we studied life history traits and their plasticities at two test ramet-densities. Plastic responses to higher test-density consisted of a shift from sexual to vegetative reproduction, and reduced flower production, plant size, branching frequency, and lengths of leaves and internodes. Plants of high-density lines tended to have longer leaves, and under high test-density branched less frequently than those of low-density lines. Directions of these selection responses indicate that the observed plastic branching response is adaptive, whereas the plastic leaf length response is not. The reverse branching frequency pattern at low test-density, where plants of high-density lines branched more frequently than those of low-density lines, indicates evolution of plasticity in branching. Moreover, when grown under less stressful low test-density, plants of high-density lines tended to grow larger than the ones of low-density lines. We conclude that ramet density affects clonal life-history evolution and that under exclusively clonal propagation clonal life-history traits and their plasticities evolve differently at different ramet densities.     

Variation in life history and genetic traits of Hawaiian mosquitofish populations

Mosquitofish (Gambusia affinis) were collected from 17 reservoirs on three islands in Hawaii, USA. Genetic and life history traits for adult females from these populations were used to evaluate hypotheses concerning short-term evolutionary divergence of populations recently established from a common ancestral source. The effects of founder events and drift on genetic variability and population differentiation were also examined. Significant differences in life history characteristics, allele frequencies, and multi-locus heterozygosities (H) were found among fish populations collected from different reservoirs and between reservoirs classified as stable or fluctuating on the basis of temporal fluctuation in water level. Females from stable reservoirs exhibited greater standard length (35.1 vs 32.8 mm), lower fecundity (11.9 vs 15.2 embryos), lower reproductive allocation (18.2% vs 22.8%), but larger mean embryo size (1.95 vs 1.67 mg) than females from fluctuating reservoirs. Consistency in means among replicates of each reservoir class and concordance in direction and magnitude of differences reported here and results of sampling conducted from these same locations 10 years previously (Stearns, 1983a) suggest that ecological factors intrinsic to these two environments are important in determing population life history traits. Females from stable reservoirs exhibited lower heterozygosity than females from fluctuating reservoirs (0.134 vs 0.158, respectively). Levels and direction od differences in heterozygosity, the high proportion of polymorphic loci and lack of fixation of alternative alleles argue against a purely stochastic explanation for genetic and life history variation among reservoir populations. Levels of genetic variability and interpopulation differentiation were similar to those observed in mainland populations of this species. A high proportion of the genetic diversity was apportioned between populations and within populations due to differences between juveniles and adults. Significant genotypic differences between adult and juvenile age classes suggest that the genetic divergence of local populations may occur over short periods of time.     

Zonation of a lentic ecotone and its correspondence to life history strategies in fish

A drainage channel network southeast of lake Neusiedl was investigated for fish species distribution. The network consists of relatively large and permanent channels providing a stable habitat for fish and smaller unstable channels drying up approximately once every five years. A consistent pattern of fish species distribution was found which could be interpreted with the help of a new triangular model of life history adaptations. In permanent channels so-called periodic and equilibrium species prevail whereas temporary channels are inhabited by opportunistic species exclusively. In the drainage channel network a number of locally endangered fish species which have disappeared from the adjacent lake during the last decades were found suggesting that the channel network functions as a refuge for these fishes.     

Effects of ocean acidification on the early life history of a tropical marine fish

Little is known about how fishes and other non-calcifying marine organisms will respond to the increased levels of dissolved CO₂ and reduced sea water pH that are predicted to occur over the coming century. We reared eggs and larvae of the orange clownfish, Amphiprion percula, in sea water simulating a range of ocean acidification scenarios for the next 50–100 years (current day, 550, 750 and 1030 ppm atmospheric CO₂). CO₂ acidification had no detectable effect on embryonic duration, egg survival and size at hatching. In contrast, CO₂ acidification tended to increase the growth rate of larvae. By the time of settlement (11 days post-hatching), larvae from some parental pairs were 15 to 18 per cent longer and 47 to 52 per cent heavier in acidified water compared with controls. Larvae from other parents were unaffected by CO₂ acidification. Elevated CO₂ and reduced pH had no effect on the maximum swimming speed of settlement-stage larvae. There was, however, a weak positive relationship between length and swimming speed. Large size is usually considered to be advantageous for larvae and newly settled juveniles. Consequently, these results suggest that levels of ocean acidification likely to be experienced in the near future might not, in isolation, significantly disadvantage the growth and performance of larvae from benthic-spawning marine fishes.     

Concordance between life history traits, invasion history, and allozyme diversity of the Everglades invader Melaleuca quinquenervia

During the century following its initial introduction in 1886, the Australian tree Melaleuca quinquenervia (Myrtaceae) dispersed from a few introduction points to occupy over 200,000 ha, primarily in historic Everglades wetlands of southern Florida. Cellulose acetate gel electrophoresis (CAGE) was used to investigate the allozyme diversity and population genetic structure of 208 individuals in a dozen populations resulting from this invasion. The analyses showed that these populations have a high (82%) rate of polymorphic loci and an average of 2 alleles/locus. There was substantial heterozygosity (mean H_e = 0.356), which concords well with recent studies reporting a greater number of introduction events and sources than generally recognized. The introduction history and distributional patterns within Florida have led to geographic structuring (G_ST = 0.419) in which the Gulf Coast metapopulation has a greater effective number of alleles and greater heterozygosity than the Atlantic Coast metapopulation. The gene diversity in M. quinquenervia was comparable to other tropical woody species. Its strong population divergence was reminiscent of pioneer species and consistent with its status as a plant invader in Florida.     

Heritability estimates of life history traits in small white butterflyPieris rapae crucivora

Heritabilities and genetic correlations of life history characters (pupal weight, age-specific fecundities, and egg weight) of small white butterfly Pieris rapae crucivora are estimated by a quantitative genetic method (sib analysis). The results indicate moderate or high heritabilities and a largely negative genetic correaltion in age-specific fecundities.     

Rapid adjustments of migration and life history in hemisphere-switching cliff swallows

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水电梯级开发进程中澜沧江干流鱼类群落演变特征

澜沧江水能资源丰富,水电梯级开发盛行。研究结合历史数据搜集和现状调查,通过对比分析,揭示了水电梯级开发进程对澜沧江干流鱼类群落影响及其机制。结果表明,梯级水电站建设进程中,澜沧江渔业产量逐步增加,与水电装机容量呈极显著正相关关系(r=0.936,P<0.01),截至目前,已增长了约8倍,达到53930 t;鱼类多样性在水电开发初期因土著鱼类的消失而明显下降,但随着外来鱼类进入鱼类多样性水平出现回升。鱼类多样性指数DG-F在梯级开发之前(<1990)、之后(2008—2013)与当前(2018—2019)分别为0.67、0.47和0.67。在水电梯级开发进程中,鱼类生境类型由急流型为主逐渐演变为了以缓流型为主,产卵类型由以产沉性卵为主逐渐演变为了以产粘性卵为主,植食性、滤食性营养类型鱼类占比逐渐增加。水电站建设后,河流流速变缓、营养物质沉降富集为浮游植物生长繁殖提供了适宜的静水条件和丰富的物质基础,促进了鱼类生物量增加。生态环境变化协同外来鱼类胁迫导致鱼类生态类型发生变异。本研究初步为水电梯级开发生态环境效应评估和鱼类多样性保护提供了理论基础。