Thermal evolution of pre-adult life history traits, geometric size and shape, and developmental stability in Drosophila subobscura

Replicated lines of Drosophila subobscura originating from a large outbred stock collected at the estimated Chilean epicentre (Puerto Montt) of the original New World invasion were allowed to evolve under controlled conditions of larval crowding for 3.5 years at three temperature levels (13, 18 and 22 degrees C). Several pre-adult life history traits (development time, survival and competitive ability), adult life history related traits (wing size, wing shape and wing-aspect ratio), and wing size and shape asymmetries were measured at the three temperatures. Cold-adapted (13 degrees C) populations evolved longer development times and showed lower survival at the highest developmental temperature. No divergence for wing size was detected following adaptation to temperature extremes (13 and 22 degrees C), in agreement with earlier observations, but wing shape changes were obvious as a result of both thermal adaptation and development at different temperatures. However, the evolutionary trends observed for the wing-aspect ratio were inconsistent with an adaptive hypothesis. There was some indication that wing shape asymmetry has evolutionarily increased in warm-adapted populations, which suggests that there is additive genetic variation for fluctuating asymmetry and that it can evolve under rapid environmental changes caused by thermal stress. Overall, our results cast strong doubts on the hypothesis that body size itself is the target of selection, and suggest that pre-adult life history traits are more closely related to thermal adaptation.     

Developmental time and size-related traits in Drosophila buzzatii along an altitudinal gradient from Argentina

Clinal analysis for fitness-related traits provides a well-known approach to investigate adaptive evolution. Several fitness-related traits (developmental time, thorax length, wing length and wing loading) were measured at two laboratory generations (G7 and G33) of D. buzzatii from an altitudinal gradient from northwestern Argentina, where significant thermal differences persist. Developmental time (DT) was positively correlated with altitude of origin of population. Further, DT was negatively correlated with maximal mean temperature at the site of origin of population, and this thermal variable decreases with altitude. Wing loading tended to be larger in highland than in lowland populations, suggesting that flight performance is subject to stronger selection pressure in highland populations. Developmental time showed a significant increase with laboratory generation number. There was no significant correlation between developmental time and body size across populations along the altitudinal cline of DT. This result illustrates that developmental time and body size do not always evolve in the same direction, even though both traits are often positively and genetically correlated in a well-known tradeoff in Drosophila.     

Direct and correlated responses to artificial selection on developmental time and wing length in Drosophila buzzatii

Abstract.— Developmental time and body size are two positively correlated traits closely related to fitness in many organisms including Drosophila . Previous work suggested that these two traits are involved in a trade-off that may result from a negative genetic correlation between their effects on pre-adult and adult fitness. Here, we examine the evolution of developmental time and body size (indexed by wing length) under artificial selection applied to one or both traits in replicated D. buzzatii populations. Directional changes in both developmental time and wing length indicate the presence of substantial additive genetic variance for both traits. The strongest response to selection for fast development was found in lines selected simultaneously to reduce both developmental time and wing length, probably as an expected consequence of a synergistic effect of indirect selection. When selection was applied in the direction opposite to the putative genetic correlation, that is, large wing length but fast development, no responses were observed for developmental time. Lines selected to reduce both wing length and developmental time diverged slightly faster from the control than lines selected to increase wing length and reduce developmental time. However, wing length did not diverge from the control in lines selected only for fast development. These results suggest a complex genetic basis of the correlation between developmental time and wing length, but are generally consistent with the hypothesis that both traits are related in a trade-off. However, we found that this trade-off may disappear under uncrowded conditions, with fast-developing lines exhibiting a higher pre-adult viability than other lines when tested at high larval density.     

The impact of elevated UV-B (280–320 nm) radiation levels on the reproduction biology of a highland and a lowland population of Silene vulgaris

A highland (altitude 1600 m) and a lowland (altitude –2 m) population of the perennial herb Silene vulgaris were tested on the effects of elevated levels of UV-B radiation on their reproductivity. Highland populations receive higher natural UV-B doses than lowland populations. Therefore adaptation to high UV-B levels of the highland population is to be expected. The lowland population showed a decrease in the number of seed producing flowers and the number of seeds produced per plant under elevated UV-B levels. The highland population increased the number of seeds per plant under elevated UV-B levels. In both populations individual seed mass as well as seed germination percentages were unaffected by the UV-B flux received by the parental plant. Possible effects of UV-B induced alterations in reproductivity on the geographical distribution of the different populations are discussed.     

BEHAVIORAL DIFFERENTIATION IN OVIPOSITION ACTIVITY IN DROSOPHILA BUZZATII FROM HIGHLAND AND LOWLAND POPULATIONS IN ARGENTINA: PLASTICITY OR THERMAL ADAPTATION?

Highland populations of several Drosophila species in Argentina were active early in the afternoon in the field as opposed to populations from a much warmer lowland site, where flies were mainly active in the early evening prior to sunset. For one of these species, Drosophila buzzatii, we tested for a genetic component of activity differences by carrying out crosses within and between populations and measuring oviposition activity of the progeny in the laboratory. We found that activity in the highland population exceeded that in the lowland one during the midafternoon, whereas activity in the lowland population exceeded that in the highland one prior to the beginning of the dark period. Oviposition activity for the period corresponding to the field observations was regressed on the proportion of the genome derived from the highland population. This variable significantly predicted oviposition activity between 1400 and 1600 and between 2000 and 2200 h. Activity of both reciprocal crosses was intermediate and not significantly different from each other, suggesting that nuclear genetic, rather than cytoplasmic factors contribute to differences in oviposition activity between the populations. Two morphological, one genetic, and one stress resistance trait were also scored to examine whether temperature differences between environments were associated with other differences between populations. Wing length of wild-caught and laboratory-reared flies from the highland population significantly exceeded that in the lowland. Thorax length of laboratory-reared flies from the highland population also significantly exceeded that from the lowland. Chromosomal inversion frequencies differed significantly between the two populations with a fivefold reduction in the frequency of arrangement 2st in the highland as compared to the lowland population. This arrangement is known for its negative dose effect on size, and thus, the highland population has experienced a genetic change, perhaps as a result of adaptation to the colder environment, where body size and the frequency of arrangement 2st have changed in concert. Finally, a heat knockdown test revealed that the lowland population was significantly more resistant to high temperature than the highland one. In conclusion, we suggest that temperature has been an important selective agent causing adaptive differentiation between these two populations. We also suggest that the activity rhythms of the two populations have diverged as a consequence of behavioral evolution, that is, through avoidance of stressful temperatures as a mean of thermal adaptation.     

Altitudinal variation in egg retention and rates of embryonic development in oviparous Zootoca vivipara fits predictions from the cold-climate model on the evolution of viviparity

The evolution of reptilian viviparity is favoured, according to the cold‐climate hypothesis, at high latitudes or altitudes, where egg retention would entail thermal benefits for embryogenesis because of maternal thermoregulation. According to this hypothesis, and considering that viviparity would have evolved through a gradual increase in the extent of intrauterine egg retention, highland oviparous populations are expected to exhibit more advanced embryo development at oviposition than lowland populations. We tested for possible differences in the level of egg retention, embryo development time and thermal biology of oviparous Zootoca vivipara near the extreme altitudinal limits of the species distribution in the north of Spain (mean altitude for lowland populations, 235 m asl.; for highland populations, 1895 m asl.). Altitude influenced neither temperature of active lizards in the field nor temperature selected by lizards in a laboratory thermal gradient, and pregnant females selected lower temperatures in the thermal gradient than did males and nonpregnant females across altitudinal levels. Eggs from highland populations contained embryos more developed at the time of oviposition (Dufaure and Hubert's stages 33–35) than eggs of highland populations (stages 30–34) and partly because of this difference incubation time was shorter for highland embryos. When analysed for clutches from both altitudinal extremes at the same embryonic stage at oviposition (stage 33), again incubation time was shorter for highland populations, indicating genuine countergradient variation in developmental rate. Our results indicate that temperature is an environmental factor affecting the geographical distribution of different levels of egg retention in Z. vivipara, as predicted by the cold‐climate hypothesis on the evolution of viviparity.     

Genetic diversity within and among populations of Diprion pini (Hym., Diprionidae) determined by random amplified polymorphic DNA-polymerase chain reaction of haploid males

Abstract: Based on haploid males, random amplified polymorphic DNA (RAPD) markers were used to study genetic variation within and among four French populations and one Finnish outgroup population of the common pine sawfly, Diprion pini (L.), representing a severe European forest pest associated with mass outbreaks. Taking into account that all multilocus haplotypes were detected, a total of 140 individuals were completely discriminated by means of 17 polymorphic markers (present or absent), which were amplified from nine selected random-decamer primers. All populations shared the same genetic types, but pronounced population-specific frequency distributions were found, indicating that on average 84% of the present genetic variation exists within populations and the remaining smaller part counts for interpopulational variation. The haplotype differentiation registered was able to distinguish between the class of lowland populations and the class of highland populations. Reproductive isolation and therefore limited altitudinal gene flow, indicated in case of a French highland population by an enlarged number of fixed markers, and hitchhiking effects with respect to selective processes at certain loci following local adaptation and speciation are discussed to explain the population structures found. A possible selection is indicated by five markers, showing significantly different frequency distributions between the class of highland populations and the class of lowland populations.     

Genetic analysis of adaptation differences between highland and lowland tropical maize using molecular markers

Molecular-marker loci were used to investigate the adaptation differences between highland and lowland tropical maize. An F₂ population from the cross of two inbred lines independently derived from highland and lowland maize germplasm was developed, and extracted F_3:4 lines were phenotype in replicated field trials at four thermally diverse tropical testing sites, ranging from lowland to extreme highland (mean growing season temperature range 13.2–24.6°C). Traits closely related with adaptation, such as biomass and grain yield, yield components, days from sowing to male and female flowering, total leaf number, plant height and number of primary tassel branches (TBN), were analyzed. A large line × environment interaction was observed for most traits. The genetic basis of this interaction was reflected by significant, but systematic, changes from lowland to highland sites in the correlation between the trait value and genomic composition (designated by the proportion of marker alleles with the same origin). Joint analysis of quantitative trait loci (QTLs) over sites detected 5–8 QTLs for each trait (except disease scores, with data only from one site). With the exception of one QTL for TBN, none of these accounted for more than 15% of the total phenotypic variation. In total, detected QTLs accounted for 24–61% of the variation at each site on average. For yield, yield components and disease scores, alleles generally favored the site of origin. Highland-derived alleles had little effect at lowland sites, while lowland-derived alleles showed relatively broader adaptation. Gradual changes in the estimated QTL effects with increasing mean site temperature were observed, and paralleled the observed patterns of adaptation in highland and lowland germplasm. Several clusters of QTLs for different traits reflected the relative importance in the adaptation differences between the two germplasm types, and pleiotropy is suggested as the main cause for the clustering. Breeding for broad thermal adaptation should be possible by pooling genes showing adaptation to specific thermal regimes, though perhaps at the expense of reduced progress for adaptation to a specific site. Molecular marker-assisted selection would be an ideal tool for this task, since it could greatly reduce the linkage drag caused by the unintentional transfer of undesirable traits. Received: 10 October 1998 / Accepted: 9 April 1999     

Immunoglobulin allotypes among Taiwan aborigines: evidence of malarial selection could affect studies of population affinity

The aborigines of Taiwan represent the indigenous inhabitants of the island at the time of the arrival of the Chinese from the mainland. Linguistically, the aboriginal Taiwanese are related to the Malayo-Polynesian-speaking inhabitants of Indonesia and the Philippines. Three tribes occupied lowland areas while six tribes occupied highland areas. Previous studies indicate that genetic markers associated with malaria occur in lowland populations. Though the GM haplotypes are demonstrated to be very useful in the measure of population affinities, the possibility of malarial selection on this locus could affect studies of population affinity. The present work is a case study to see whether a subdivided insular population under a possible selective load will provide divergent clustering analysis depending on the population sampled. Immunoglobulin allotype (GM and KM) profiles were generated on 230 lowland and 407 highland Taiwan Aborigines from the nine tribes. A highly significant difference in GM haplotype distribution was detected between lowland and highland populations (adjusted G = 69.408, 2 df [degrees of freedom], p < 0.00001). There were no significant differences in KM*1 frequency by altitude. The Taiwan Aboriginal GM and KM frequencies were compared to data from Indonesians, Vietnamese, Thai, Malay, Chinese from Taiwan, and Ryukyu Islanders from Okinawa using cluster analysis. The lowland populations plot among the Thai (N, NC) and Malayan Aborigines. In contrast, the highland and total Taiwan Aborigine samples plot with the Indonesian, Vietnamese, and Malayan Negrito samples. Thus, depending on the populations of Taiwan Aborigines used, different conclusions could be reached. The highland population supports the published linguistic ties; however, the lowland population does not support the linguistic relationship with Indonesian populations but is more closely related to Thai and Malays, or reflects a similar selection history.     

Genetic diversity and differentiation of cultivated amochi (Arisaema schimperianum Schott) in Ethiopia as revealed by AFLP markers

Amochi (Arisaema schimperianum Schott) is an off-season crop plant in southern Ethiopia, grown during the dry season on residual moisture, for its edible tubers. It has gained importance as a "security crop" especially during the years of moisture stress and food shortage. Amochi is irritating in contact to the skin. Removal of this effect is an important question for breeding. As the first step, however we attempt to establish base line information of its breeding system and genetic variability using AFLPs. The extent of genetic differentiation among 11 populations (96 individuals) of amochi sampled along altitudinal gradients that varied from 1700 to 3200 m a.s.l. was investigated. The populations were classified in to three altitudinal groups: lowland (1700 to 2200 m a.s.l.), central-highland (2201 to 2600 m a.s.l.) and highland (2601 to 3200 m a.s.l.). Polymorphic loci (167) scored from four primer pair combinations, were used for principal component analysis (PCA), and analysis of molecular variance (AMOVA). Both PCA and unweighed pair group with arithmetic mean (UPGMA) clearly differentiated populations into their respective altitude groups, with large genetic distances. AMOVA analysis revealed 70.5%, 16.7% and 12.8% variability between altitude groups, between populations and within populations respectively. Average diversity indices within populations were also low. Since the largest proportion of variation is located between altitude groups, rather than within populations, we suggest future studies on the chemical composition, low irritation, and other desirable traits should consider populations from different altitude ranges.     

Genetic variation and covariation among life history traits in populations of Acanthoscelides obtectus maintained on different hosts

We explored the extent to which two populations of Acanthoscelides obtectus (Coleoptera: Bruchidae), maintained in the laboratory for about 60 generations on common bean (Phaseolus vulgaris) and chickpea (Cicer arietinum) seeds, differ genetically in life history traits. Using a half-sib breeding design, we screened for genetic variation in oviposition preference for two hosts within both populations, and examined whether this variation is correlated with weevil pre-adult (egg-to-adult viability and egg-to-adult developmental time) and adult (female fecundity and longevity) fitness components on these two hosts. Significant differences between the Phaseolus and Cicer population were detected in viability, developmental time and oviposition preference, but not in female fecundity and longevity. The absence of a significant population × host interaction in all traits, except for developmental time in males, indicates that the Cicer population has not attained the status of host race. The estimated narrow-sense heritabilities within population within host plant were in the low-to-moderate level (range: 1%–79%), with an overall average of about 24%. Within the population maintained on the chickpeas we detected significant genetic correlations between female developmental time on chickpea seeds and preference for chickpeas. In the population maintained on the primary host of this weevil species (the Phaseolus population) we found no significant preference/performance genetic correlations. Data are also presented on the genetic correlations of preference and performance across host seeds within both populations. These correlations are found to be positive for all traits in both populations, indicating the absence of trade-offs in either performance or behavioural response that might impose selection for host specialization within populations.     

Variation in UV sensitivity among common frog Rana temporaria populations along an altitudinal gradient

Solar ultraviolet-B (UV-B) radiation can be harmful for developing amphibians. As the UV-B dose increases with altitude, it has been suggested that high-altitude populations may have an increased tolerance to high levels of UV-B radiation as compared to lowland populations. We tested this hypothesis with the common frog (Rana temporaria) by comparing populations from nine altitudes (from 333 to 2450m above sea level). Eggs collected in the field were used for laboratory experiments, i.e., exposed to high levels of artificial UV-B radiation. Eggs were reared at 14+/-2 degrees C and exposed to UV treatments until hatching. Embryonic developmental rates increased strongly and linearly with increasing altitude, suggesting a genetic capacity for faster development in highland than lowland eggs. Body length at hatching varied significantly with UV-B treatments, being lower when eggs developed under direct UV-B exposure. Body length at hatching also increased as the altitude of populations increased, but UV-B exposure times were shorter as altitude of population increased. However, the body length difference between exposed and non-exposed individuals in each population decreased as altitude of populations increased, suggesting a costly effect of UV exposure on growth. Type of UV exposure did not influence the mean rates of embryonic mortality and deformity, but both mortality and deformity rates increased as the altitude of populations increased (while UV-B exposure duration decreased). The effect of UV-B on body length at hatching, mortality, and deformities suggests that the sensitivity to UV-B varied among populations along the altitudinal gradient. These results are discussed in evolutionary terms, specifically the potential of R. temporaria high-altitude populations to develop local genetic adaptation to high levels of UV-B.     

Trait‐specific consequences of inbreeding on adaptive phenotypic plasticity

Environmental changes may stress organisms and stimulate an adaptive phenotypic response. Effects of inbreeding often interact with the environment and can decrease fitness of inbred individuals exposed to stress more so than that of outbred individuals. Such an interaction may stem from a reduced ability of inbred individuals to respond plastically to environmental stress; however, this hypothesis has rarely been tested. In this study, we mimicked the genetic constitution of natural inbred populations by rearing replicate Drosophila melanogaster populations for 25 generations at a reduced population size (10 individuals). The replicate inbred populations, as well as control populations reared at a population size of 500, were exposed to a benign developmental temperature and two developmental temperatures at the lower and upper margins of their viable range. Flies developed at the three temperatures were assessed for traits known to vary across temperatures, namely abdominal pigmentation, wing size, and wing shape. We found no significant difference in phenotypic plasticity in pigmentation or in wing size between inbred and control populations, but a significantly higher plasticity in wing shape across temperatures in inbred compared to control populations. Given that the norms of reaction for the noninbred control populations are adaptive, we conclude that a reduced ability to induce an adaptive phenotypic response to temperature changes is not a general consequence of inbreeding and thus not a general explanation of inbreeding–environment interaction effects on fitness components.     

Ingested energy differs between populations of the toad Bufo bankorensis from different altitudes

We measured ingested energy (E(i)) and apparent digestibility efficiency (ADE) in two populations of Bufo bankorensis from different altitudes at three temperatures and during two seasons to test the hypothesis that the optimal temperature range (T(opt)) for E(i) and ADE has shifted to the lower range in highland toads and winter toads. The T(opt) for E(i) was 22 degrees C for the lowland and highland toads and did not vary between seasons, thus falsifying the hypothesis. ADE of the toads was 96%-99% at 15 degrees -30 degrees C, and there was no difference between populations or seasons. Furthermore, when fed with fast-moving prey, the toads from both altitudes had similarly low E(i) at 15 degrees C; when fed with slow-moving prey, the highland toads increased E(i) at 15 degrees C, but the lowland toads did not. These results suggest that the toads from different altitudes had different appetites, even though their feeding locomotion was hampered in both populations at low temperatures.     

Different trends of neighboring populations of Lesser Kestrel: Effects of climate and other environmental conditions

The sensitivity of population trends to the climate and environment is generally considered a species-specific trait. However, evidence that populations may show different responses to the climate and environmental conditions is growing. Whether this differential sensitivity may arise even among neighboring populations remains elusive. We compared the trends of two neighboring populations of the Lesser Kestrel Falco naumanni, using data from a 12-year survey of 158 colonies in Sicily, Italy; the two populations inhabiting a lowland and an highland area, respectively. Population trends were modeled through the TRIM algorithms implemented in R (package rtrim). A reversed U-shaped population trend was observed in the lowland, while the highland population showed oscillations around a stable trend. Sahel rainfall 2 years before each annual survey significantly affected population variation in the lowland, while rainfall in March and an index of primary productivity in the breeding areas affected population variation in the highland. This suggests that the population in the lowland may be limited mainly by winter survival in Sahel, because the lowland may be an optimal breeding area for this species. In contrast, the highland population, which occupies a different part of the climatic niche of the species, may be limited mainly by reproductive output, because rainfall in March and the primary productivity in May could represent prey availability immediately before and during the breeding months. Overall, our findings suggest that population-specific environmental sensitivity might occur even over small (<100 km) geographical scales, highlighting the need for population-specific conservation strategies.     

Changes in body melanisation and desiccation resistance in highland vs. lowland populations of D. melanogaster

Wild caught samples of Drosophila melanogaster from five highland localities showed parallel changes in melanisation and desiccation resistance in darker versus lighter phenotypes, i.e. darker flies (>45% melanisation) showed significantly higher desiccation resistance than lighter flies (<30% melanisation). In order to find an association between body melanisation and desiccation resistance, highland and lowland populations from tropical and subtropical regions (11.15-31.06 degrees N) of the Indian subcontinent were raised and investigated at 21 degrees C for four physiological traits, i.e. per cent body melanisation, desiccation resistance, rate of water loss and rate of water absorption. On the basis of mother-offspring regression, body melanisation and desiccation resistance showed higher heritability (0.58-0.68) and thus these traits are suitable for laboratory analyses. Significantly higher melanisation as well as desiccation resistance were observed in highland populations as compared with lowland populations. The rates of water loss as well as absorption were negatively correlated with body melanisation, i.e. darker flies from highlands showed a reduced rate of water loss as well as a lower rate of water absorption while the reverse trend was observed in lighter flies from lowlands. On the basis of multiple regressions, significant effects due to combined altitude and latitude were observed for all the four physiological traits. Local climatic conditions (i.e. annual average temperature and relative humidity) helped in explaining parallel changes in body melanisation and desiccation resistance in D. melanogaster.     

Variation of life-history and morphometrical traits in Drosophila buzzatii and Drosophila simulans collected along an altitudinal gradient from a Canary island

Variation in three life‐history traits (developmental time, preadult viability and daily female productivity) and five morphometrical traits (thorax length, wing length, wing width, wing/thorax ratio and wing‐aspect ratio) was studied at three developmental temperatures (20, 25 and 30 °C) in Drosophila buzzatii and Drosophila simulans collected on the island of La Gomera (Canary Archipelago). The flies originated from five closely situated localities, representing different altitudes (from 20 to 886 m above sea level) and a range of climatic conditions. We found statistically significant population effects for all traits in D. buzzatii and for most of the traits in D. simulans. Although no correlations of trait values with altitude were detected, geographical patterns for three life‐history traits and body size in D. buzzatii indicated that short‐range geographical variation in this species could be maintained by local climatic selection. Five of eight traits showed population‐by‐temperature interactions either in D. buzzatii or in D. simulans, but in all cases except wing width in D. buzzatii this could not be interpreted as adaptive responses to thermal conditions in the localities. The range of plastic changes across temperatures for particular traits differed between species, indicating a possibility for different levels of environmental stress experienced by the natural populations. The reaction norm curves and the response of within‐population variability to thermal treatments suggested better adaptations to higher and lower temperatures for D. buzzatii and D. simulans, respectively. The levels of among‐population differentiation depended on developmental temperature, implying environmental effects on the expression of the genetic variance. At 20 and 25 °C, interpopulation variability in D. buzzatii was higher than in D. simulans, while at 30 °C the opposite trend was observed. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84 , 119–136.     

Temperature and genotypic effects on life history and fluctuating asymmetry in a field strain of Culex pipiens

Fluctuating asymmetry (FA) has been proposed as a tool to measure levels of stress experienced by populations of organisms during development. To be of value as a bio-marker to highlight conditions at particular sites, it is important that variation in FA is due to environmental (eg pollution) variation and not genetic variation among populations and families, in other words heritability for FA should be very close to zero. A full-sib design was set up in which families of Culex pipiens mosquitoes collected from the field were reared at three different developmental temperatures. The effects of temperature and family on developmental rate, egg to adult survival and four wing morphological measures were assessed. There was both a temperature and a family effect on development rate and survival. Temperature affected all four wing traits, but an influence of family was only evident in two of the wing traits. Two separate measures of FA for each of the wing traits were obtained. The mean estimates of FA were mainly around 1% of the value of the character measured. There was evidence of an increase in FA with increase in temperature stress. Heritability was estimated for the wing traits and wing trait FA's using restricted estimation maximum likelihood. The estimates of heritability for the wing traits were small and, individually, did not differ significantly from zero. There was also no evidence of heritable genetic variation for any of the wing trait FA's. The results are discussed in relation to other studies where FA heritabilities have been estimated and in relation to the use of FA as an indicator of environmental stress.     

High-performing plastic clones best explain the spread of yellow monkeyflower from lowland to higher elevation areas in New Zealand

The relative contribution of adaptation and phenotypic plasticity can vary between core and edge populations, with implications for invasive success. We investigated the spread of the invasive yellow monkeyflower, Erythranthe gutatta in New Zealand, where it is spreading from lowland agricultural land into high-elevation conservation areas. We investigated the extent of phenotypic variation among clones from across the South Island, looked for adaptation and compared degrees of plasticity among lowland core versus montane range-edge populations. We grew 34 clones and measured their vegetative and floral traits in two common gardens, one in the core range at 9 m a.s.l. and one near the range-edge at 560 m a.s.l. Observed trait variation was explained by a combination of genotypic diversity (as identified through common gardens) and high phenotypic plasticity. We found a subtle signature of local adaptation to lowland habitats but all clones were plastic and able to survive and reproduce in both gardens. In the range-edge garden, above-ground biomass was on average almost double and stolon length almost half that of the same clone in the core garden. Clones from low-elevation sites showed higher plasticity on average than those from higher elevation sites. The highest performing clones in the core garden were also top performers in the range-edge garden. These results suggest some highly fit general-purpose genotypes, possibly pre-adapted to New Zealand montane conditions, best explains the spread of E. gutatta from lowland to higher elevation areas.     

Lowland panmixia versus highland disjunction: genetic and bioacoustic differentiation in two species of East African White-eye birds

East-African mountain forest species often occur in small and isolated populations, whereas species inhabiting the dry lowland savannahs exist in large and interconnected population networks. Taxa with closely related highland and lowland species, such as the East-African White-eye birds, allow testing for the potential effects of the two contrasting distribution patterns, mountain disjunction versus lowland panmixia. In this study, we compare the population genetic and bioacoustic differentiation of two representatives of the genus Zosterops: Zosterops poliogaster is exclusively found in forests at higher elevations; in comparison, Zosterops abyssinicus, only occurs in the dry and warm lowland savannahs. Both species were analysed across a similar geographical scale. Population genetic differentiation was inferred using the same set of 15 polymorphic microsatellite loci for both species. In addition, we quantitatively analyzed bioacoustic traits. Both data sets indicate a strong population differentiation among populations of the highland species, but an absence of differentiation in the lowland species. In addition, the lowland Z. abyssinicus was characterised by a twofold higher genetic diversity than detected for the highland Z. poliogaster. These two contrasting intraspecific population structures may reflect the opposite ecology and distribution of these species: the strong population isolation of Z. poliogaster resulting from long-term restriction to the cool and moist mountain forests at higher elevations has led to strong differentiation among local populations and resulted in a comparatively low level of intraspecific variability. In contrast, population panmixia in the lowland Z. abyssinicus provides a high level of gene flow allowing the maintenance of high genetic diversity and avoiding strong population structuring. These findings need to be considered when planning conservation actions.