三种同域分布喉毛花的繁殖分配

以青藏高原高寒草甸中三种同域分布的喉毛花为研究对象,通过比较三个种的植株性状和繁殖分配,探讨繁殖分配的种间差异及其与植株个体大小的关系。结果表明:(1)三个种的植株高度、顶花大小和单株花数目、繁殖分配均存在种间差异,这可能与其各自的交配系统和具体的生境以及相应的生活史对策有关;(2)在三种喉毛花中,投入到营养器官和繁殖器官的绝对资源量均呈显著正相关,未检测到植株生长和繁殖间的权衡关系;(3)三个种的个体大小与繁殖器官生物量均呈显著正相关,而与繁殖分配均呈显著负相关,这表明个体越大,繁殖投入越高,而繁殖分配越低,与以往研究结果一致,这可能是由于繁殖分配与个体大小之间存在异速关系。     

Resource competition and patterns of sexual reproduction in sympatric sibling rotifer species

We present experimental data on the reproduction patterns of three sympatric sibling rotifer species, belonging to the Brachionus plicatilis complex, as they compete for food. Variation existed in the amount and pattern of sexual reproduction among the three cyclical parthenogenetic species. Competitive exclusion between the three Brachionus species was related to a higher investment in sexual reproduction by the inferior competitor. In general, no correlation was found between sexual reproduction and population density in a given species. However, when pairs of competing species were compared, a negative relationship between sexual investment differences (between species) and average population density differences was frequently found. From the results we conclude that: (1) the characteristic sexual pattern of each species has some implications for the competitive outcome; (2) allocation of resources into sexual reproduction does not mediate coexistence; and (3) the response of sexual reproduction to competitive interaction is unlikely to determine competition outcome. Nevertheless, our results suggest that the competitively inferior species invests more in sexual reproduction, as a response to resource limitation, which would accelerate its exclusion.     

Virulence and competitive ability in an obligately killing parasite

Mixed infections are thought to have a major influence on the evolution of parasite virulence. During a mixed infection, higher within‐host parasite growth is favored under the assumption that it is critical to the competitive success of the parasite. As within‐host parasite growth may also increase damage to the host, a positive correlation is predicted between virulence and competitive success. However, when parasites must kill their hosts in order be transmitted, parasites may spend energy on directly attacking their host, even at the cost of their within‐host growth. In such systems, a negative correlation between virulence and competitive success may arise. We examined virulence and competitive ability in three sympatric species of obligately killing nematode parasites in the genus Steinernema. These nematodes exist in a mutualistic symbiosis with bacteria in the genus Xenorhabdus. Together the nematodes and their bacteria kill the insect host soon after infection, with reproduction of both species occurring mainly after host death. We found significant differences among the three nematode species in the speed of host killing. The nematode species with the lowest and highest levels of virulence were associated with the same species of Xenorhabdus, indicating that nematode traits, rather than the bacterial symbionts, may be responsible for the differences in virulence. In mixed infections, host mortality rate closely matched that associated with the more virulent species, and the more virulent species was found to be exclusively transmitted from the majority of coinfected hosts. Thus, despite the requirement of rapid host death, virulence appears to be positively correlated with competitive success in this system. These findings support a mechanistic link between parasite growth and both anti‐competitor and anti‐host factors.     

Adaptation to salinity inHordeum jubatum L. populations studied using reciprocal transplants

Tillers and seedlings ofHordeum jubatum L. from three sites with contrasting salinity regimes in central Saskatchewan, Canada were reciprocally transplanted in order to examine the tolerance of populations of this species to salinity and related habitat factors. Survival, growth and fecundity of the three populations were controlled more by transplant site characteristics than by genetic differences, i.e. differences among populations at a site tended to be smaller than differences among sites. Survival, growth and reproduction of all three populations were best at the non-saline site. The population originating at the non-saline site showed the poorest growth in the two saline habitats, but still had substantial salt tolerance. Fecundity was greatest when the populations were grow at their site of origin.     

Home ranges of parthenogenetic and bisexual species in a community of Darevskia lizards (Reptilia: Lacertidae)

We analysed the home ranges of a community of Darevskia rock lizards composed of a bisexual species (D. valentini), two parthenogens (D. armeniaca and D. unisexualis), and two backcross forms between bisexual and unisexual forms. We estimated home range areas of ink-marked, GPS-located lizards using Minimum Convex Polygon (MCP) and 95% of the locations for those individuals with five or more sightings. The bisexual D. valentini was the species with the largest home ranges, distances travelled, and the most intersections. No differences between unisexual species and backcrosses were recorded for any comparison. In males, home range size and perimeter were related to morphological characteristics. Contrary to what has been described in allopatry, unisexual species showed smaller home ranges and fewer overlaps than sympatric bisexual species. We tentatively suggest that the presence of potential bisexual partners might increase sexual competition among parthenogenetic females while differences in habitat use should also be considered.     

Salinity and Temperature Effects on Physiological Responses of <Emphasis Type="Italic">Vibrio fischeri</Emphasis> from Diverse Ecological Niches

Vibrio fischeri is a bioluminescent bacterial symbiont of sepiolid squids (Cephalopoda: Sepiolidae) and monocentrid fishes (Actinopterygii: Monocentridae). V. fischeri exhibit competitive dominance within the allopatrically distributed squid genus Euprymna, which have led to the evolution of V. fischeri host specialists. In contrast, the host genus Sepiola contains sympatric species that is thought to have given rise to V. fischeri that have evolved as host generalists. Given that these ecological lifestyles may have a direct effect upon the growth spectrum and survival limits in contrasting environments, optimal growth ranges were obtained for numerous V. fischeri isolates from both free-living and host environments. Upper and lower limits of growth were observed in sodium chloride concentrations ranging from 0.0% to 9.0%. Sepiola symbiotic isolates possessed the least variation in growth throughout the entire salinity gradient, whereas isolates from Euprymna were the least uniform at <2.0% NaCl. V. fischeri fish symbionts (CG101 and MJ101) and all free-living strains were the most dissimilar at >5.0% NaCl. Growth kinetics of symbiotic V. fischeri strains were also measured under a range of salinity and temperature combinations. Symbiotic V. fischeri ES114 and ET101 exhibited a synergistic effect for salinity and temperature, where significant differences in growth rates due to salinity existed only at low temperatures. Thus, abiotic factors such as temperature and salinity have differential effects between free-living and symbiotic strains of V. fischeri, which may alter colonization efficiency prior to infection.     

Food availability as a major driver in the evolution of life‐history strategies of sibling species

Life‐history theory predicts trade‐offs between reproductive and survival traits such that different strategies or environmental constraints may yield comparable lifetime reproductive success among conspecifics. Food availability is one of the most important environmental factors shaping developmental processes. It notably affects key life‐history components such as reproduction and survival prospect. We investigated whether food resource availability could also operate as an ultimate driver of life‐history strategy variation between species. During 13 years, we marked and recaptured young and adult sibling mouse‐eared bats (Myotis myotis and Myotis blythii) at sympatric colonial sites. We tested whether distinct, species‐specific trophic niches and food availability patterns may drive interspecific differences in key life‐history components such as age at first reproduction and survival. We took advantage of a quasi‐experimental setting in which prey availability for the two species varies between years (pulse vs. nonpulse resource years), modeling mark‐recapture data for demographic comparisons. Prey availability dictated both adult survival and age at first reproduction. The bat species facing a more abundant and predictable food supply early in the season started its reproductive life earlier and showed a lower adult survival probability than the species subjected to more limited and less predictable food supply, while lifetime reproductive success was comparable in both species. The observed life‐history trade‐off indicates that temporal patterns in food availability can drive evolutionary divergence in life‐history strategies among sympatric sibling species.     

Is salinity tolerance the key to success for the invasive water bug <Emphasis Type="Italic">Trichocorixa verticalis</Emphasis>?

Trichocorixa verticalis is a North American water bug (Heteroptera: Corixidae) that occurs in brackish and saline aquatic systems. Recently, it has been found invading three continents including Europe. Its invasive success has been attributed to the capacity of tolerating hypersalinity. We compared both the realized and standardized salinity niche of invasive T. verticalis and native Corixidae to verify if T. verticalis may fill in an unoccupied niche. We first established the field distribution of T. verticalis and native Corixidae along a salinity gradient. Second, we experimentally tested the salinity tolerance of T. verticalis and three common native Corixidae species. Of the seven Corixidae species found in the field study, three were positively related to the salinity gradient: S. selecta, S. stagnalis, and T. verticalis. T. verticalis showed the highest salinity optimum, however, after correcting for environmental background variation, salinity optima differed little among the three halophilic species. In the salinity tolerance experiment, S. selecta outperformed T. verticalis, which performed as well as S. stagnalis. Based on our experimental results, we cannot support the hypothesis that T. verticalis’ invasion is mediated by a high salinity tolerance that allows this species to colonize habitats unoccupied by native Corixidae. Although these findings contrast with the field patterns in which T. verticalis showed the highest niche optimum and tolerance, these patterns may have been partly due to other environmental factors, particularly anthropogenic disturbance. Our comparative results are for adults only, and it remains possible that relative salinity tolerance patterns for juveniles differ from that for adults, which may add to the observed field pattern.     

Population and reproductive dynamics of the polychaete Pygospio elegans in a boreal estuary complex

Pygospio elegans is an opportunistic, wide‐spread spionid polychaete that reproduces asexually via fragmentation and can produce benthic and pelagic larvae, hence combining different developmental modes in one species. We documented the density, size distribution, and reproductive activity of P. elegans at four sites in the Danish Isefjord‐Roskilde Fjord estuary complex, where all modes of reproduction were reported. We compared population dynamics of this species to environmental parameters such as salinity, temperature, and sediment characteristics (grain size, sorting, porosity, water content, organic content, C/N). We observed that new cohorts—resulting either from sexual or asexual reproduction—appeared in spring and fall, and old ones disappeared in late summer and winter. Sexual reproduction occurred from September until May, and although their timing was variable, there were two reproductive peaks at three sites. At those sites, we also observed a switch in larval developmental mode. Asexual reproduction peaked in April. While the seasonal dynamics can be related to temperature to a large extent, the differences in population dynamics among sites also correlated with sediment structure and salinity. Populations from sites with coarse and heterogeneous sediment had high levels of sexual reproduction. At the site with lower salinity, intermediate and benthic larvae were present during winter in contrast to pelagic larvae found at the other sites. However, we could not identify one clear environmental factor determining the mode of development. At present, it remains unclear to what degree genetic background contributes to mode of development. Hence, whether the differences in developmental mode are the result of genetically different cohorts will be further investigated.     

Local biotic adaptation of trees and shrubs to plant neighbors

Natural selection as a result of plant–plant interactions can lead to local biotic adaptation. This may occur where species frequently interact and compete intensely for resources limiting growth, survival, and reproduction. Selection is demonstrated by comparing a genotype interacting with con‐ or hetero‐specific sympatric neighbor genotypes with a shared site‐level history (derived from the same source location), to the same genotype interacting with foreign neighbor genotypes (from different sources). Better genotype performance in sympatric than allopatric neighborhoods provides evidence of local biotic adaptation. This pattern might be explained by selection to avoid competition by shifting resource niches (differentiation) or by interactions benefitting one or more members (facilitation). We tested for local biotic adaptation among two riparian trees, Populus fremontii and Salix gooddingii, and the shrub Salix exigua by transplanting replicated genotypes from multiple source locations to a 17 000 tree common garden with sympatric and allopatric treatments along the Colorado River in California. Three major patterns were observed: 1) across species, 62 of 88 genotypes grew faster with sympatric neighbors than allopatric neighbors; 2) these growth rates, on an individual tree basis, were 44, 15 and 33% higher in sympatric than allopatric treatments for P. fremontii, S. exigua and S. gooddingii, respectively, and; 3) survivorship was higher in sympatric treatments for P. fremontii and S. exigua. These results support the view that fitness of foundation species supporting diverse communities and dominating ecosystem processes is determined by adaptive interactions among multiple plant species with the outcome that performance depends on the genetic identity of plant neighbors. The occurrence of evolution in a plant‐community context for trees and shrubs builds on ecological evolutionary research that has demonstrated co‐evolution among herbaceous taxa, and evolution of native species during exotic plants invasion, and taken together, refutes the concept that plant communities are always random associations.     

No differential consequences of reproduction according to sex in Juniperus communis var. depressa (Cupressaceae)

In dioecious plant species, males and females are thought to have dissimilar allocation patterns. Females are believed to invest more in reproduction and less in growth and maintenance than males. This differential investment between sexes could result in distinct growth patterns and contrasting survival rates, thereby affecting the sex ratio of a population and the age and size distribution of males and females, possibly leading to habitat segregation according to sex. These effects might become more apparent under particularly limiting conditions, such as in nutrient-deficient soils or in climatically stressed environments. To verify these predictions, growth patterns, microsite characteristics, and age and size distribution of male and female individuals were compared, and population sex ratio was determined in three populations of the dioecious shrub Juniperus communis var. depressa (Cupressaceae, Pinophyta) along a short latitudinal gradient on the eastern coast of Hudson Bay (Northern Québec, Canada). We found that the northernmost population had a male-biased sex ratio, but that the southernmost one had a higher proportion of females. Our results failed to reveal any significant differences in radial growth patterns, mean sensitivity, annual elongation of the main axis, and size and age frequency distribution between males and females in any population. Furthermore, there was no evidence of microhabitat segregation according to sex as indicated by the lack of differences in the physicochemical characteristics of the substrate under males and females. Clearly, the expected ecological consequences of a presumed greater investment of females in reproduction were not apparent even under the very stressful conditions prevailing on subarctic dunes. Many factors could reduce differences in the cost of reproduction between males and females, such as the number and quality of reproductive structures produced annually by individuals of each sex, the possible photosynthetic activity of the immature female cones, and the complexity of the source/sink relationship within individuals. Alternatively, there may be no differences between sexes in their reproductive investment.     

Restricted gene flow within and between rapidly diverging Neotropical plant species

Speciation involves the evolution of traits and genetic differences that contribute to reproductive isolation and the cessation of gene flow, and studying closely related species and divergent populations gives insight into how these phenomena proceed. Here, we document patterns of gene flow within and between two members of a rapid Neotropical species radiation, Costus pulverulentus and Costus scaber (Costaceae). These species co‐occur in the tropical rainforest and share pollinators, but are reproductively isolated by a series of prezygotic barriers, some of which show evidence of reinforcement at sympatric sites. Here, we genotype microsatellite markers in plants from eight sites that span the geographical range of both species, including four sympatric sites. We also genotype putative hybrids found at two sympatric sites. We find high levels of genetic isolation among populations within each species and low but detectable levels of introgression between species at sympatric sites. Putative hybrids identified by morphology are consistent with F1 or more advanced hybrids. Our results highlight the effectiveness of prezygotic isolating mechanisms at maintaining species boundaries in young radiations and provide empirical data on levels of gene flow consistent with reinforcement.     

Mating Preferences of the Gynogenetic Amazon Molly Differ Between Populations Sympatric with Different Host Species

Gynogenetic species rely on sperm from heterospecifics for reproduction but do not receive genetic benefits from mating because none of the paternal genome is incorporated into offspring. The gynogenetic Amazon molly (Poecilia formosa) is a species of hybrid origins that are sympatric with one of the two parent species that provide sperm for reproduction, P. latipinna or P. mexicana. Amazons should not prefer to mate with one species over the other because sperm from both species will trigger embryogenesis, but mating preferences may be present in Amazons through other mechanisms. Amazons may prefer the more familiar species (males found in sympatry), or Amazons may prefer males with the greatest lateral projection area (LPA), a preference that is present in the parent species and may be retained within the Amazon hybrid genome. We tested association preferences of two populations of Amazons sympatric with either P. mexicana or P. latipinna. We first performed live trials to test whether Amazons preferred one host species over the other and found that neither population of Amazons showed a preference. We then tested whether Amazons preferred sympatric male (familiar) host or the male with the greatest lateral projection area (LPA) using four animated male models that varied in host species and manipulation of LPA. We found Amazons from a population sympatric with P. latipinna showed no variation in their association preference across the different models. In contrast, Amazons from a population sympatric with P. mexicana (naturally small LPA) spent more time associating with the male models that had smaller LPA, which is more familiar to this population of Amazons. We suggest that Amazons may have population differences in mating preferences, where Amazons sympatric with P. latipinna may not show mating preference for host species, but Amazons sympatric with P. mexicana may show preferences for more familiar‐shaped males.     

Coexistence of bisexual and unisexual populations of Nysius groenlandicus in the Zackenberg Valley,Northeast Greenland

The seed‐feeding true bug Nysius groenlandicus (Zetterstedt) (Heteroptera: Lygaeidae) has temperature and humidity preferences similar to many desert‐inhabiting insects. Nevertheless, it is widely distributed in Greenland and occurs even in high arctic areas. This seeming paradox implies that the species has developed physiological, ecological, and behavioral mechanisms that enable it to cope with the extreme arctic environment. One of these adaptations is its ability to reproduce both sexually and asexually. Sexual reproduction is most common in coastal populations, whereas asexual reproduction (parthenogenesis) occurs mainly in inland populations. Preliminary data from the Zackenberg Valley in Northeast Greenland indicated that both reproductive strategies occurred within the same area. We therefore decided to focus on this area to find evidence of (1) coexistence of unisexual and bisexual populations, (2) factors that correlate with the distribution of the two reproductive types, and (3) morphological differences between females from sexual and asexual populations. We sampled N. groenlandicus at 51 sites within the Zackenberg area. Males and females were found in almost equal numbers in only four of the samples, and only in samples taken close to the coast line, whereas samples from the inner part of the valley consisted almost entirely of females. Thus, the distribution of uni‐ and bisexual populations at the local scale agreed with the pattern previously found for Greenland as a whole. Using data obtained from two climate stations operated in the area, we showed that average summer temperatures tend to be more favorable for N. groenlandicus in the inner part of the valley than at the coast. The inland populations inhabited small isolated patches, whereas the sexual populations were found in the more homogeneous areas along the coast. Data support the hypothesis that coexistence of the two reproductive types is maintained by a combination of environmental variability, which gives sexual reproduction an advantage, and metapopulation dynamics characterized by frequent extinctions and re‐colonizations, which favors asexual reproduction. Head width of females from unisexual populations was on average 7% larger than that of females from bisexual populations. The mechanism behind this morphological difference needs further investigation.     

The taxonomy of some British Littorina species, with notes on their reproduction (Mollusca: Prosobranchia)

The rough periwinkle Littorina saxatilis is considered, in current literature, to consist of various sympatric "subspecies" and "varieties". These, it has been suggested, are incipient species and are evidence for sympatric speciation.
This paper shows that in Wales the "saxatilis" aggregate consists of four separate, fully sympatric species: L. rudis, patula, nigrolineata and neglecta . Differences between these species include proportions, sculpture and size of the shell, range of colour patterns, the anatomy of the genitalia, and isozyme patterns. The possible evidence for incipient species is discussed and rejected.
The diversity of penis form amongst the British winkles is remarkable, and it is suggested that in these sympatric species the structure of the penis could be of importance in species recognition.
The four species occupy different zones on the shore and three certainly differ also in their methods of reproduction: L. rudis is ovoviviparous and contains embryos throughout the year, patula is ovoviviparous but contains embryos only in winter, nigrolineata is oviparous. The reproduction and dispersal methods of all British winkles are reviewed. The evidence available supports the view that non-planktonic dispersal is an adaptation which, in species whose shell colour varies considerably from one locality to another, enables each population to become adapted to its local environmental conditions. Ovoviviparity occurs in high-shore non-planktonic species, and may be an adaptation to avoid the dangers of egg desiccation. Planktonic dispersal is found in species whose shell colour does not vary as much as in non-planktonic ones. In these species, it is argued that a common planktonic pool enables a rapid re-colonization in the case of local decrease in population numbers, and also the rapid dispersal of successful mutations.     

Divergent parasite infections in sympatric cichlid species in Lake Victoria

Parasitism has been proposed as a factor in host speciation, as an agent affecting coexistence of host species in species‐rich communities and as a driver of post‐speciation diversification. Young adaptive radiations of closely related host species of varying ecological and genomic differentiation provide interesting opportunities to explore interactions between patterns of parasitism, divergence and coexistence of sympatric host species. Here, we explored patterns in ectoparasitism in a community of 16 fully sympatric cichlid species at Makobe Island in Lake Victoria, a model system of vertebrate adaptive radiation. We asked whether host niche, host abundance or host genetic differentiation explains variation in infection patterns. We found significant differences in infections, the magnitude of which was weakly correlated with the extent of genomic divergence between the host species, but more strongly with the main ecological gradient, water depth. These effects were most evident with infections of Cichlidogyrus monogeneans, whereas the only host species with a strictly crevice‐dwelling niche, Pundamilia pundamilia, deviated from the general negative relationship between depth and parasitism. In accordance with the Janzen–Connell hypothesis, we also found that host abundance tended to be positively associated with infections in some parasite taxa. Data on the Pundamilia sister species pairs from three other islands with variable degrees of habitat (crevice) specialization suggested that the lower parasite abundance of P. pundamilia at Makobe could result from both habitat specialization and the evolution of specific resistance. Our results support influences of host genetic differentiation and host ecology in determining infections in this diverse community of sympatric cichlid species.     

Similarities,differences, and seasonal patterns in the diets ofEulemur rubriventer andEulemur fulvus rufus in the Ranomafana National Park,Madagascar

I studied the diets of two sympatric species ofEulemur (E. fulvus rufus andE. rubriventer) in the Ranomafana National Part in southeastern Madagascar from July 1988 through August 1989. Both species were highly frugivorous throughout the year and devoted similar amounts of time to feeding daily; the composition of their diets were similar. Three aspects of both lemur species' diets were correlated with seasonal food availability: changes in interspecific dietary overlap, the length of feeding bouts, and the amount of time devoted to feeding daily. Throughout the year neither species had a more diverse or more folivorous diet than its sympatric congener. However, there were several consistent year-round differences between their diets.E. f. rufus initiated more feeding bouts daily that were shorter in duration than those ofE. rubriventer. E. f. rufus also consistently exploited more unripe fruits and mature leaves thanE. rubriventer did throughout the study.E. f. rufus migrated from the study site during a period of fruit scarcity. These dietary patterns are discussed here in regard to feeding patterns observed in other sympatric congeneric primate species, whether these dietary differences can contribute to these two species' ability to coexist, and how differences in diet may be influenced by differences in social structure. I suggest that subtle, consistent differences in diet and seasonal dietary differences are sufficient to allow these two species to coexist.     

Cytological evidence for temporal differences during the asynchronous ovarian maturation of bisexual and unisexual fishes of the genus Poecilia

Comparisons based upon morphological features and cytochemical staining properties of chromatin, nucleoli, and the ooplasm were used in the present analysis of ovarian maturation in wild-caught Poecilia mexicana and its related gynogenetic diploid and triploid' species'. Using an empirically derived ovarian maturation index, seasonal and collection site differences were found between the unisexual and bisexual forms. These fish seem equally suited to their environments. However, our data indicate that differences in microhabitat can have a profound influence on oocyte development. Although females of Poecilia spp. have asynchronous cycles of ovarian maturation, we could not detect any peculiar cytological events associated with the gynogenetic mode of reproduction. Sperm were found in ovaries of both unisexual and bisexual forms indicating that the unisexuals can compete effectively with females of P. mexicana for matings with males of this species. The methods employed in this study provide a sensitive measure of reproductive potentials in sympatric species.     

Nesting habitat use and partitioning of three sympatric ninespine sticklebacks (genus <Emphasis Type="Italic">Pungitius</Emphasis>): implications for reproductive isolation

The nest site characteristics and distribution patterns of nests of three sympatric ninespine sticklebacks, the brackish- and fresh-water types and Pungitius tymensis, were investigated in the Shiomi River, eastern Hokkaido, Japan. In this river, most of the males of the brackish-water type were found to build their nests in the lower reach with higher salinity (mean 13.5‰) and water temperature (mean 13.3°C), whereas the males of the freshwater type and P. tymensis built their nests in the upper reach with lower salinity (mean 0.6 and 0.8‰, respectively) and water temperature (both mean 11.3°C). The ranges of their nesting areas, however, overlapped within the river, because the nests of the brackish-water type were widely distributed in the river. A comparison of the nest site characteristics in the area where nest overlapped indicated that there were no significant differences for all of five characteristics (the distance from the nest to the shore, the distance from the nest to the bottom, the distance to the nearest nest, the nest density and the amount of cover around the nest). Using canonical discriminant analysis, the nests of the three sticklebacks could not be distinguished using the five nest characteristics. These results suggest that habitat isolation through physical factors functions as an important mechanism of reproductive isolation between the brackish-water type and the other two sticklebacks.     

Sensitivity of Daphnia species to phosphorus-deficient diets

The life history of freshwater cladocerans such as Daphnia spp. is strongly affected by their environment. Factors such as temperature, food quantity and even the presence or absence of predators influence growth, reproduction and morphology of individuals. Recently, it has also become clear that the quality of the food can affect various life history traits of Daphnia. More specifically, the effect of the elemental composition of algae, expressed as the C:P ratio, has been studied intensively. Daphnia species differ in their response to differences in the C:P ratio of their food. Until now, it has been unclear whether these species differences are driven by phylogenetic constraints or by adaptation to particular environmental conditions. Here we present laboratory experiments with 12 Daphnia species from three different subgenera originating from a broad range of habitats. We compared somatic growth rates and sensitivity to variation in the nutrient stoichiometry of the food with habitat parameters, taking into account the phylogenetic history of the species. No associations between fitness and habitat parameters were detected. However, we found a trade-off between sensitivity to P-deficient diets and the maximum growth rate on a P-sufficient diet. In several cases, this trade-off helps to explain the association between species distribution and habitat parameters. We observed no correlation of the sensitivity to P limitation with the phylogenetic history of the genus Daphnia. Thus, we conclude that the differential responses among Daphnia species to variation in P content in food were driven mainly by adaptations to their local habitats, and are not constrained by deep evolutionary patterns.