Cost of reproduction as reduced growth in genotypes of two congeneric species with contrasting life histories

Summary We examined the effect of reproduction on growth in 33 genotypes of Plantago major and 14 genotypes of P. rugelii. These two herbaceous perennials have contrasting life histories; P. major reproduces at a smaller size, and allocates a larger proportion of its biomass to reproduction, than P. rugelii. The effect of reproduction on frowth was determined experimentally using photoperiod manipulations to control level of reproduction. The difference in growth between reproductive treatments was divided by the difference in capsule weight to produce a measure of reproductive cost per g of capsule for genotypes of the two species. In both species there was substantial variation among genotypes in the effect of reproduction on growth. Much of this variation could be correlated with differences among genotypes in the extent of reproductive investment and plant size. Cost in terms of reduction in growth per g of capsule increased with reproductive investment in P. rugelii, and with plant size in P. major. We suggest the differences between species in timing and extent of reproduction are related to the differences between species in effect of reproduction on growth. Plantago rugelii may reproduce to a lesser extent than P. major because cost per g of capsule in terms of reduced vegetative biomass, increases with reproductive output in the former species, but not in the latter. Similarly, P. major may reproduce earlier than P. rugelii because cost per g of capsule increases with plant size in P. major, but not in P. rugelii.     

Geographical patterns of genetic structure in marine species with contrasting life histories

Aim  Phylogeographical breaks may reflect historical or present-day impediments to gene flow, and the congruence of these breaks across multiple species lends insight into evolutionary history and connectivity among populations. In marine systems, examining the concordance of phylogeographical breaks is challenging due to the varied sampling scales in population genetics studies and the diverse life histories of marine organisms. A quantitative approach that considers the effects of sampling scale and species life history is needed.
Location  The south-east and south-west coasts of the United States.
Methods  We quantitatively analysed previously published datasets of marine fauna to look for concordance among phylogeographical breaks. We used a bootstrap approach to determine the regions where phylogeographical breaks are more common than expected by chance among species with planktonic dispersal as well as those with restricted dispersal.
Results  On the south-west coast, breaks were clustered near Point Conception among planktonic dispersers and near Los Angeles among restricted dispersers. On the south-east coast, breaks were most common near the southern tip of Florida for planktonic dispersers and near Cape Canaveral for restricted dispersers.
Main conclusions  Dispersal ability is an important determinant of phylogeographical patterns in marine species. Breaks among planktonic dispersers on both coasts are congruent with present-day flow-mediated barriers to dispersal, suggesting that phylogeographical structure in species with planktonic larvae may reflect contemporary oceanography, while breaks in restricted dispersers reflect historical processes. These results highlight the importance of explicitly considering sampling scale and life history when evaluating phylogeographical patterns.     

Profiles of enzyme activity in larvae of two cyprinid species with contrasting life styles (Cyprinidae; Teleostei)

Growth and the development of gills, muscle fibres and 10 enzymes serving different metabolic functions were studied in larvae of Rutilus rutilus (L.) and Chalcalburnus chalcoides (Agassiz, 1832). R. rutilus starts swimming and feeding one to three days after hatching, whereas in C. chalcoides this process is delayed by about 10 days. This difference in behaviour is reflected in the time-course of growth, the differentiation of the red muscle fibres and the activity of the enzymes of aerobic energy metabolism. On the other hand, the activity of the enzymes of anaerobic energy metabolism increases steadily throughout the period of observation (up to 60 days post-hatch), this trend being more pronounced in C. chalcoides than in R. rutilus . A weight-independent and a weight-dependent phase of development can be distinguished in the enzymes of aerobic energy metabolism. It is suggested that, in accord with previous findings, the early phase of locomotor activity of cyprinid larvae is fuelled mainly by aerobic processes, and that the central muscle mass of the larvae is more aerobic than the white muscle fibres of the adults. The delayed development of aerobic enzyme activity in C. chalcoides is compensated by the accelerated development of anaerobic enzyme activity, particularly of creatine kinase and lactate dehydrogenase. This difference between the two species studied suggests differences in the metabolic basis of burst activity.     

Sexual interference in two Chamerion species with contrasting modes of movement herkogamy

Evolution of herkogamy has been ascribed to preventing autonomous selfing within flowers, but this argument has received challenges due to the negative effects of sexual interference on reproductive success of plant species. We examined the effects of the two contrasting modes of herkogamy, detailed by the different patterns of style movement, on the foraging time of pollinators on flowers, pollen removal, and deposition in two Chamerion species. Our results suggested that the duration of foraging time of bumblebees was generally higher in C. angustifolium (L.) Holub than in C. conspersum (Hausskn.) Holub during the male-phase of flowers, but the reverse during the female-phase of flowers. As a result, stigma interfered with pollen removal more in C. conspersum than in C. angustifolium, based on examinations of pollen removal after one visit by a pollinator. However, this negative effect on total pollen removal was covered by the high pollinator diversity and the possible high visitation rate in the study sites. In contrast, we found that almost no difference existed in pollen deposition rate after one visit of a pollinator between the two Chamerion species, and emasculation did not increase the total pollen deposition in either species, indicating that anthers did not interfere with pollen deposition in the two Chamerion species. Our results suggested that, compared with C. conspersum, the derived mode of herkogamy in C. angustifolium reduced interference of stigmas in pollen removal. This might contribute to the wide distribution of C. angustifolium, to some degree, in environments of pollinator scarcity and low activity in newly colonized habitats.     

Age-independent telomere length predicts fitness in two bird species

Telomeres are dynamic DNA-protein structures that form protective caps at the ends of eukaryotic chromosomes. Although initial telomere length is partly genetically determined, subsequent accelerated telomere shortening has been linked to elevated levels of oxidative stress. Recent studies show that short telomere length alone is insufficient to induce cellular senescence; advanced attrition of these repetitive DNA sequences does, however, reflect ageing processes. Furthermore, telomeres vary widely in length between individuals of the same age, suggesting that individuals differ in their exposure or response to telomere-shortening stress factors. Here, we show that residual telomere length predicts fitness components in two phylogenetically distant bird species: longevity in sand martins, Riparia riparia, and lifetime reproductive success in dunlins, Calidris alpina. Our results therefore imply that individuals with longer than expected telomeres for their age are of higher quality.     

Spatial extent of bird species response to landscape changes: colonisation/extinction dynamics at the community-level in two contrasting habitats

Animal community dynamics in changing landscapes are primarily driven by changes in vegetation structure and ultimately by how species respond to these changes and at which spatial scale. We consider two major components of local community dynamics, species colonisation and extinction. We hypothesise that (1) the optimal spatial extent needed to accurately predict them will differ between these two processes; (2) it will also likely differ from species to species as a result of life history traits differences related to differences in habitat selection and (3) that a species' primary habitat will determine the spatial extent at which it perceives change in vegetation structure. We used data collected over 25 yr in a changing Mediterranean landscape to study bird species local colonisation and extinction patterns in two groups of species typical from two habitats: open farmland and woodland. Vegetation changes were measured at spatial extents ranging from 0.2 to 79 ha. Local species colonisation and extinction estimates were computed using a method accounting for heterogeneity in detection probability among species. We built linear models between local species colonisation/extinction estimates and vegetation changes and examined variations in model quality with respect to the spatial extent at which vegetation changes had been measured. Models for open habitat species showed that colonisation processes operated at the landscape scale (79 ha), while extinction was more tightly linked to local habitat requirements (0.2 ha). Models for woodland species presented a low and constant model quality whatever the spatial extent considered. Our results suggest that the dynamics of the woodland species considered responded to a combination of vegetation changes at several scales and, in particular, to changes in the vertical structure of the vegetation. We highlight the need to explicitly consider spatial extent in studies of habitat selection and of habitat and population dynamics to improve our understanding of the biological consequences of land use changes and guide more effective conservation efforts.     

Cluster root formation and function vary in two species with contrasting geographic ranges

Plant and Soil - Southern South American Proteaceae can occupy soils that are rich in total phosphorus (P) but poor in available P (for example volcanic soils) thanks to their cluster roots (CR),...     

Spatial genetic structure of two sympatric neotropical palms with contrasting life histories

The spatial genetic structure within sympatric populations of two neotropical dioecious palm species with contrasting life histories was characterized to evaluate the influence of life history traits on the extent of genetic isolation by distance. Chamaedorea tepejilote is a common wind-pollinated arboreal understory palm. Chamaedorea elatior is an uncommon climbing subcanopy palm with entomophilous pollination syndrome. A total of 59 allozyme alleles for C. tepejilote and 53 alleles for C. elatior was analyzed using both unweighted (Iu) and weighted (Iw) Moran's I spatial autocorrelation statistics. The spatial genetic structure detected within these populations is consistent with those reported for highly dispersed plants. A significance test for differences between mean Moran's I-coefficients revealed less spatial genetic structure within the C. tepejilote population than that in the C. elatior population. Adjacent individuals of C. elatior exhibited significant spatial genetic autocorrelation (Iu=0.039, Iw=0.034), indicating a Wright's neighborhood size of about 100 individuals. For C. tepejilote, nonrandom genetic distribution among nearest neighbors was detected, even from small spatial autocorrelation values (Iu=0.008, Iw=0.009), consistent with a neighborhood size of about 300 individuals. For both species, seed dispersal, mortality among life cycle stages, overlapping generations, and contrasting traits of mating and reproduction influence the standing spatial genetic structure within populations.     

Driving forces shaping phytoplankton assemblages in two subtropical plateau lakes with contrasting trophic status

1. We studied driving forces shaping phytoplankton assemblages in two subtropical plateau lakes with contrasting trophic status, the oligotrophic deep Lake Fuxian and the eutrophic shallow Lake Xingyun. 2. Phytoplankton samples were taken monthly for a year and phytoplankton species were sorted into the main taxonomic groups and associations proposed by Reynolds. A canonical correspondence analysis (CCA) was used to test the occurrence of these classification schemes and to determine their discriminatory power. 3. The results suggest that the major driving forces in Lake Fuxian were physical variables, and particularly the underwater light climate, whereas, nutrients were the important driving force in Lake Xingyun. 4. Top–down control through zooplankton grazing in Lake Fuxian was hardly ever a significant determinant itself, because of the scarcity of zooplankton and their low grazing efficiency of predation while a dominance of inedible cyanobacteria throughout the year rendered top–down controls ineffective failing in Lake Xingyun. Hence phytoplankton communities in both lakes appear to be regulated primarily by bottom–up controls.     

Seasonal life history trade-offs in two leafwing butterflies: Delaying reproductive development increases life expectancy

Surviving inhospitable periods or seasons may greatly affect fitness. Evidence of this exists in the prevalence of dormant stages in the life cycles of most insects. Here I focused on butterflies with distinct seasonal morphological types (not a genetic polymorphism) in which one morphological type, or form, delays reproduction until favorable conditions return, while the other form develops in an environment that favors direct reproduction. For two butterflies, Anaea aidea and A. andria, I tested the hypothesis that the development of each seasonal form involves a differential allocation of resources to survival at eclosion. I assayed differences in adult longevity among summer and winter forms in either a warm, active environment or a cool, calm environment. Winter form adults lived 40 times longer than summer form but only in calm, cool conditions. The magnitude of this difference provided compelling evidence that the winter form body plan and metabolic strategy (i.e. resource conservatism) favor long term survival. This research suggests that winter form adults maintain lowered metabolic rate, a common feature of diapause, to conserve resources and delay senescence while overwintering.     

Inbreeding depression in two species of Mimulus (Scrophulariaceae) with contrasting mating systems

We examined the effect of self- and cross-pollination on germination success, flowering probability, pollen and ovule production, survivorship, and adult aboveground biomass in two species of Mimulus with contrasting mating systems: the highly seifing M. micranthus and an outcrossing population of M. guttatus. Cross-pollinations were performed both within and between populations in order to examine the scale at which the genetic load is distributed. We found significant inbreeding depression in M. guttatus in four of the six traits, with the highest inbreeding depression observed in biomass (68% and 69% based on within- and between-population crosses, respectively) and lowest in ovule production (21% based on between-population crosses only). M. micranthus displayed significant inbreeding depression in only two of the six traits examined. Again, we observed the highest inbreeding depression in biomass (47–60% based on within- and between-population crosses, respectively), but both traits showing significant differences between self and outcross progeny expressed lower inbreeding depression than in M. guttatus. We detected no significant inbreeding depression for either pollen or ovule production in M. micranthus. An estimate of total inbreeding depression based on the multiplicative effects of all traits was also lower in M. micanthus than∗∗∗ in M. guttatus. Our results are consistent with the expected purging of genetic load in populations with high selfing rates. The absence of inbreeding depression in M. micranthus pollen and ovule production, two traits with strong links to fitness in a selfing annual, further suggests the important role of directional selection in determining the population's genetic load. Comparison of cross-pollinations made within and between populations revealed little evidence of divergence of genetic load among the M. micranthus and M. guttatus populations examined.     

Nutrient foraging traits in 10 co-occurring plant species of contrasting life forms

1 Responses to spatial heterogeneity of soil nutrients were tested in 10 plant species that differ in life form and successional status, but which co-occur in the South Carolina coastal plain. The morphological responses of the root system were tested by assessing scale (represented by root mass and root length densities), precision (preferential proliferation of roots in nutrient-rich patches compared with less fertile patches) and discrimination (ability to detect and proliferate within the richest patches when patches vary in nutrient concentration). We also investigated sensitivity (growth benefits gained as spatial heterogeneity of nutrients increases, measured as total biomass).
2 Ten individuals of each species were grown in pots under four treatments that had differing nutrient distribution but the same overall nutrient addition. Plants were harvested when roots reached pot edge.
3 We observed high variation between species in scale, precision and sensitivity. No significant discrimination responses were observed, although greatest root mass density occurred at intermediate fertility levels for all species.
4 We rejected the hypothesis that scale and precision are negatively correlated. Indeed, in herbaceous species alone, scale and precision were positively correlated.
5 Sensitivity was not closely related to precision, indicating that proliferation of roots in fertile patches does not always yield growth benefits in heterogeneous soils. Further, some sensitive species had very low precision, suggesting that a positive growth response in heterogeneous environments may be related to plasticity in physiology or root life span, rather than morphology.
6 Plant life form was not correlated with precision or sensitivity. However, scale of response was greater in herbs than in woody plants, possibly because the two life forms develop root systems at different rates.     

Patterns of morphological variation in two sexually dimorphic bird species with different tail shapes

Many studies have focused on tail ornamentation in birds, but not all tail shapes have been studied in depth. Graduated and pin tails have received less attention than forked tails, despite being more likely, in terms of aerodynamic theory, to be honest signals. We report morphological variation in live specimens of two sexually dimorphic passerines from the same site with different tail shapes: graduated (Cape sugarbird Promerops cafer ) and pin (orange-breasted sunbird Antobaphes violacea ). Coefficients of variation (CVs) were calculated for all morphological traits, both non-ornamental (range 1.91–5.72) and ornamental (range 5.83–21.71). Males and females did not differ in CV for any non-ornamental trait. Ornamental traits in males of both species were significantly more variable than all non-ornamental traits. Cape sugarbird ornamental traits were significantly more variable than those of orange-breasted sunbirds. The high levels of variation in graduated tails relative to pintails suggest that these traits have been driven mainly by sexual selection. In contrast, both constraining natural and multiple ornament selection could be responsible for the relatively low levels of variation in pintails.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 437–443.     

Differential antioxidant response between two Symbiodinium species from contrasting environments

High sea surface temperature accompanied by high levels of solar irradiance is responsible for the disruption of the symbiosis between cnidarians and their symbiotic dinoflagellates from the genus Symbiodinium. This phenomenon, known as coral bleaching, is one of the major threats affecting coral reefs around the world. Because an important molecular trigger to bleaching appears related to the production of reactive oxygen species (ROS), it is critical to understand the function of the antioxidant network of Symbiodinium species. In this study we investigated the response of two Symbiodinium species, from contrasting environments, to a chemically induced oxidative stress. ROS produced during this oxidative burst reduced photosynthesis by 30 to 50% and significantly decreased the activity of superoxide dismutase. Lipid peroxidation levels and carotenoid concentrations, especially diatoxanthin, confirm that these molecules act as antioxidants and contribute to the stabilization of membrane lipids. The comparative analysis between the two Symbiodinium species allowed us to highlight that Symbiodinium sp. clade A temperate was more tolerant to oxidative stress than the tropical S. kawagutii clade F. These differences are very likely a consequence of adaptation to their natural environment, with the temperate species experiencing conditions of temperature and irradiance much more variable and extreme.     

Bioacoustics for species management: two case studies with a Hawaiian forest bird

The management of animal endangered species requires detailed information on their distribution and abundance, which is often hard to obtain. When animals communicate using sounds, one option is to use automatic sound recorders to gather information on the species for long periods of time with low effort. One drawback of this method is that processing all the information manually requires large amounts of time and effort. Our objective was to create a relatively “user‐friendly” (i.e., that does not require big programming skills) automatic detection algorithm to improve our ability to get basic data from sound‐emitting animal species. We illustrate our algorithm by showing two possible applications with the Hawai'i ‘Amakihi, Hemignathus virens virens, a forest bird from the island of Hawai'i. We first characterized the ‘Amakihi song using recordings from areas where the species is present in high densities. We used this information to train a classification algorithm, the support vector machine (SVM), in order to identify ‘Amakihi songs from a series of potential songs. We then used our algorithm to detect the species in areas where its presence had not been previously confirmed. We also used the algorithm to compare the relative abundance of the species in different areas where management actions may be applied. The SVM had an accuracy of 86.5% in identifying ‘Amakihi. We confirmed the presence of the ‘Amakihi at the study area using the algorithm. We also found that the relative abundance of ‘Amakihi changes among study areas, and this information can be used to assess where management strategies for the species should be better implemented. Our automatic song detection algorithm is effective, “user‐friendly” and can be very useful for optimizing the management and conservation of those endangered animal species that communicate acoustically.