Isolated Island Populations Research Articles

Seasonal dynamics of three inquiline species in isolated island populations of Sarracenia purpurea L. in Lake Michigan

AbstractA seasonal survey of the abundances of three inquilines species in Sarracenia purpurea L. leaves was conducted by sampling 240 leaves from three pitcher plant populations on Beaver Island in Lake Michigan, United States. Leaf characteristics such as fluid pH, fluid volume, and keel length were quantified. The study focused primarily on the larvae of three dipteran inquiline species – the midge, Metriocnemus knabi Coquillet, the mosquito, Wyeomyia smithii (Coquillet), and the flesh fly, Fletcherimyia fletcheri Aldrich. Dipteran inquiline abundances varied with sampling season. Most pitchers contained one of the three studied inquilines species. Mosquito abundances were low relative to the other inquilines. In samples collected soon after new leaves open, a mixture of mosquito and midge larvae was characteristic. We related inquilines abundances to leaf parameters using generalized linear mixed models. The midge and mosquito responded differently to leaf parameters during different sampling seasons, where as the flesh fly showed no response. The most important leaf parameters were pH and percent of total leaf volume filled with fluid (relative volume). The midge and mosquito were more likely to be present in pitchers with low pH and higher fluid volume. Our results indicate that pitchers of isolated northern populations of S. purpurea are inhabited by a less diverse insect community than reported elsewhere. Our study also suggests that site isolation may play an important role in the seasonal variation of inquiline community structure.

Differentiation with drift: a spatio-temporal genetic analysis of Galápagos mockingbird populations (Mimusspp.)

Small and isolated island populations provide ideal systems to study the effects of limited population size, genetic drift and gene flow on genetic diversity. We assessed genetic diversity within and differentiation among 19 mockingbird populations on 15 Galápagos islands, covering all four endemic species, using 16 microsatellite loci. We tested for signs of drift and gene flow, and used historic specimens to assess genetic change over the last century and to estimate effective population sizes. Within-population genetic diversity and effective population sizes varied substantially among island populations and correlated strongly with island size, suggesting that island size serves as a good predictor for effective population size. Genetic differentiation among populations was pronounced and increased with geographical distance. A century of genetic drift did not change genetic diversity on an archipelago-wide scale, but genetic drift led to loss of genetic diversity in small populations, especially in one of the two remaining populations of the endangered Floreana mockingbird. Unlike in other Galápagos bird species such as the Darwin's finches, gene flow among mockingbird populations was low. The clear pattern of genetically distinct populations reflects the effects of genetic drift and suggests that Galápagos mockingbirds are evolving in relative isolation.

Island selection on mammalian life-histories: genetic differentiation in offspring size

BackgroundSince Darwin's pioneering work, evolutionary changes in isolated island populations of vertebrates have continued to provide the strongest evidence for the theory of natural selection. Besides macro-evolutionary changes, micro-evolutionary changes and the relative importance of natural selection vs. genetic drift are under intense investigation. Our study focuses on the genetic differentiation in morphological and life-history traits in insular populations of a small mammal the bank vole Myodes glareolus.ResultsOur results do not support the earlier findings for larger adult size or lower reproductive effort in insular populations of small mammals. However, the individuals living on islands produced larger offspring than individuals living on the mainland. Genetic differentiation in offspring size was further confirmed by the analyses of quantitative genetics in lab. In insular populations, genetic differentiation in offspring size simultaneously decreases the additive genetic variation (VA) for that trait. Furthermore, our analyses of differentiation in neutral marker loci (Fst) indicate that VA is less than expected on the basis of genetic drift alone, and thus, a lower VA in insular populations could be caused by natural selection.ConclusionWe believe that different selection pressures (e.g. higher intraspecific competition) in an insular environment might favour larger offspring size in small mammals. Island selection for larger offspring could be the preliminary mechanism in a process which could eventually lead to a smaller litter size and lower reproductive effort frequently found in insular vertebrates.

Phylogeography of the Galápagos hawk ( Buteo galapagoensis): A recent arrival to the Galápagos Islands

Galápagos hawks ( Buteo galapagoensis) are one of the most inbred bird species in the world, living in small, isolated island populations. We used mitochondrial sequence and nuclear minisatellite data to describe relationships among Galápagos hawk populations and their colonization history. We sampled 10 populations (encompassing the entire current species range of nine islands and one extirpated population), as well as the Galápagos hawk’s closest mainland relative, the Swainson’s hawk ( B. swainsoni). There was little sequence divergence between Galápagos and Swainson’s hawks (only 0.42% over almost 3 kb of data), indicating that the hawks colonized Galápagos very recently, likely less than 300,000 years ago, making them the most recent arrivals of the studied taxa. There were only seven, closely related Galápagos hawk haplotypes, with most populations being monomorphic. The mitochondrial and minisatellite data together indicated a general pattern of rapid population expansion followed by genetic isolation of hawk breeding populations. The recent arrival, genetic isolation, and phenotypic differentiation among populations suggest that the Galápagos hawk, a rather new species itself, is in the earliest stages of further divergence.

Effects of isolation on distribution, fecundity, and survival in the self-incompatible Achillea millefolium (L.)

In this study I investigate how isolation affects fecundity in a self-incompatible plant species, Achillea millefolium (L.), on islands in the Stockholm archipelago. According to preliminary results, the distribution pattern of A. millefolium in this region is affected by both patch size and isolation; this was more thoroughly investigated. Individuals were transplanted to non-isolated and isolated islands, keeping resource availability, population size, and inter-individual spacing constant. I examined whether reproductive success in isolated island populations is reduced compared to non-isolated populations, and if so, whether this is due to pollen limitation. The germinability of the seeds was also investigated, along with seed predation and survival. I found no significant difference in pollen deposition and fecundity between individuals on non-isolated and isolated islands. Furthermore, there were no differences in seed germinability, seed predation, and survival associated with isolation. The fecundity of A. millefolium in this region is unaffected by pollinator availability as isolation increases. A generalist pollinator fauna may ensure persistence in isolated habitats where more specialised pollinator services are unreliable during the flowering season.

Dynamics of a clinal hybrid zone and a comparison with island hybrid zones of flycatchers (Ficedula hypoleuca and F. albicollis)

AbstractBreeding data for pied flycatchers Ficedula hypoleuca and collared flycatchers F. albicollis, from 47 localities in the Czech Republic and Slovakia, were analysed. We show that co‐existence and hybridization were mainly restricted to a rather narrow, latitudinal cline. The distribution of the two flycatchers coincides with topography and habitat, collared flycatchers dominating in warmer habitats than pied flycatchers. Maintained co‐existence within the same locality was the exception rather than the rule and most matings occurred in allopatry. In sympatry hybridization occurred at a frequency that was much lower than expected from random mating. Hybrids had low hatching success but some hybrids were apparently fertile. Shortage of conspecific mates may explain why individual birds engage in mixed species pairs. The proportion of pied flycatchers that was involved in mixed pairs was high and increased with decreasing relative frequencies of pied flycatchers in the population. The proportion of collared flycatchers involved in mixed pairs was low, reflecting the higher relative frequency of this species in most mixed populations. Comparisons suggest that fewer hybrids are breeding in the Central European, clinal hybrid zone than in the isolated hybrid zones of the Baltic Isles. Moreover, hybrid fertility was apparently higher in the island zones than in the clinal zone. We suggest that more extensive introgression in the isolated island populations has resulted in an increase in hybrid fitness by an accumulation of fertile individuals of mixed ancestry (i.e. F2, F3 … Fn‐hybrids) acting as bridges for gene exchange. Differences in the dynamics of the two classes of hybrid zones, especially in pattern of gene flow, may explain these differences in frequency and fertility of hybrids.

Evolutionary Differentiation in Three Endemic West Indian Warblers

We explored the evolution of geographic distributions in archipelagos by comparing mitochondrial DNA (mtDNA) sequences and morphometric characters within and among conspecific populations of Adelaide's Warbler (Dendroica adelaidae), Plumbeous Warbler (D. plumbea), and Olive-capped Warbler (D. pityophila). Phylogenetic reconstructions were based upon 1,455 nucleotides of protein-coding mtDNA sequence from 53 individual warblers; morphological analyses employed three external measurements from a larger number of museum specimens. Of the three taxa studied, Adelaide's Warbler occupied the broadest and most fragmented geographical distribution and exhibited the greatest inter-population differentiation in both mtDNA and morphology. Phylogenetic analyses demonstrated that the three Adelaide's Warbler populations are each reciprocally monophyletic with the Puerto Rican lineage basal to sister clades on Barbuda and St. Lucia. Genetic distances among these populations were comparable with those between some continental species. In contrast to the mtDNA pattern, the Puerto Rican and Barbudan Adelaide's Warbler populations were most similar in morphometry. We observed considerably less mtDNA and morphometric differentiation among populations of the two species with more restricted and less fragmented distributions, the Plumbeous Warbler of Dominica and Guadeloupe and the Olive-capped Warbler of the Bahamas and Cuba. High levels of molecular and morphological differentiation among the geographically disjunct Adelaide's Warbler populations and low differentiation in the two species with less fragmented ranges suggest that range disjunctions indicate the long-term evolutionary independence of geographically isolated island populations.

Power laws governing epidemics in isolated populations.

Temporal changes in the incidence of measles virus infection within large urban communities in the developed world have been the focus of much discussion in the context of the identification and analysis of nonlinear and chaotic patterns in biological time series. In contrast, the measles records for small isolated island populations are highly irregular, because of frequent fade-outs of infection, and traditional analysis does not yield useful insight. Here we use measurements of the distribution of epidemic sizes and duration to show that regularities in the dynamics of such systems do become apparent. Specifically, these biological systems are characterized by well-defined power laws in a manner reminiscent of other nonlinear, spatially extended dynamical systems in the physical sciences. We further show that the observed power-law exponents are well described by a simple lattice-based model which reflects the social interaction between individual hosts.

Vertebrate extinction in Mediterranean islets: an example from Cyprus

B/OGEOGRAPHIA — vol. XVIII — 1995 (Pubblicato il 31 ottobre 1996) Le piccole Isole Circumsarde e il loro significato Biogeografico Vertebrate extinction in Mediterranean islets: an example from Cyprus E. HADJISTERKOTIS” and B. MASALAM‘ qqOfi’zqcer of tlae Game zzml Fauna Service, Mzfiirtry of Interior; Nzrorzkz, Cyprus. ”°qI7zrz‘z'tzIte of General P/Jyrziology mm’ Biological C/Jemzirtry, Faculty of Bz'0logz'czzl Sciences, U72z'verrz'z‘y of Sczsrarz; Szzsrarz; Italy Key words: Vertebrate, extintion, mediterranean islets, Cyprus. SUMMARY Cyprus is the third island in the Mediterranean \vith an area of 9.251 Kmz. Is a 15 million year old island of oceanic origin which has never been connected to the mainland. In this study we attempt to tally all the extinctions that took place on the island of Cyprus and compare the emerging pattern with that of other islands. All the endemic animals recorded from the Pleistocene Fauna, the Pygmy hippopotamus P/Ja/zoz.trz'0s /7zz'IIzIl‘m', the Pygmy elephant Elzzp/Mr cypria/ax, the Cyprus genet Gezzetta /7/er/rtoizler, and the Ancient Cypriot shrew Crociclzzm rzzzzueole/zr [mu/c_vpI'1‘a, are extinct. These animals represent 60% of the endemic mammalian species aver recorded in Cyprus and 20% of the endemic subspecies. From the Archaeological Fauna nine taxa of animals were reported, which (with the exception of the Cyprus mouflon Oz;/: gmelz'm' op/Jz'0Iz) are not present today. From the avifauna two species and seven subspecies (12% of the total number of breeding taxa) were noted as endemic. Two of the latter, the Dipper C/‘uclz/r rinclz/5 oly/up/qcur is extinct and the Raven Coruzzr camx cjvprizzr is in danger of extinction. This pattern of extinction of indigenous spe— cies was also observed on other islands and is a consequence of small isolated island populations. INTRODUCTION A characteristic of modern extinctions of birds and mammals is that they are concentrated on islands (Diamond, 1984). For birds, 171 species and sub- species have become extinct since 1600, and over 90 percent of these extinc- tions have occurred on islands. For mammals out of 115 documented historic extinctions, 36 percent of these have occurred on islands. This pattern is in part due to the nature of island populations. They are small and isolated; thus they cannot recover from local extirpation following environmental perturba- tions or long—term climatic changes by immigration from other areas (MacArthur and \Wilson, 1967; Leigh, 1981). A growing body of evidence for birds and mammals indicates that over the last few thousand years, the most important agent of direct change in the envi- ronments is human disturbance and alteration of habitats (Diamond, 1984). Most extinct species in recorded history are attributed to some aspects of human interference, such as: habitat destruction; human hunting; effects of introduced taxa particularly predators, and trophic cascades (i.e., secondary extinctions caused by previous extinctions; Diamond and Case, 1986). Usually the period immediately following the initial settlement of islands is correlated 691

Spatial Genetic Structure among Korean Populations ofCamellia japonicaandEurya japonica(Theaceae)

AbstractCamellia japonicaandEurya japonica, broad‐leaved evergreen woody plants, are widely distributed in eastern Asia.Eurya japonicais dioecious, whereas flowers ofC. japonicaare perfect. We investigated the spatial distribution of genotypes among 15 and 21 Korean populations ofC. japonicaandE. japonicausing spatial autocorrelation analysis of enzyme polymorphisms to test the previous prediction that dioecy is a primary factor which increases interpopulational gene flow. The patterns of spatial genetic distribution among populations of both species are very similar: percentage of significant Moran's /values (15 vs. 17 forC. japonicaandE. japonica) and percentage of significant overall correlogram (18 vs. 20 forC. japonicaandE. japonica). For both species, the patterns of average Moran's/values for each distance class were very similar as in an isolation by distance model. It may be concluded that dioecy may not a primary factor in shaping spatial genetic structure inE. japonica.Instead, abundant and continuously distributed patterns observed inE. japonicaand an occasional pollen transfer by birds between isolated island populations ofC. japonicain Korea may play roles in shaping spatial genetic structure among Korean populations of the two species.

Mycobacterial and fungal skin sensitivity patterns among remote population groups in Papua New Guinea, and in the New Hebrides, Solomon, and Caroline Islands.

Simultaneous intradermal sensitivity testing to Mycobacterium tuberculosis (PPD-S), six different atypical mycobacteria (PPD-A, B, F, G, T, and Y), Coccidiosides immitis (coccidioidin), and Histoplasma capsulatum (histoplasmin) was performed on 560 subjects among the relatively isolated island populations of Ifaluk (Caroline Islands), Loh and Merig (New Hebrides), Anuta (Solomon Islands), and in the Mala (Amdei) and Iwane (Simbari) villages of the Anga linguistic groups in the Marawaka area of the Eastern Highlands Province of Papua New Guinea. At the time these tests were performed (Mala and Iwane villages, and Ifaluk Atoll in 1967, and Loh, Merig, and Anuta Islands in 1972), all island populations had already had a long history of sporadic European contact, whereas the New Guinean villages of Mala and Iwane had remained virtually unexposed to the outside world. Using a dose of 0.001 mg PPD per 0.0 ml (5 TU), and considering induration of at least 10 mm at 48 hours to represent a positive reaction, skin sensitivity to M. tuberculosis was found to be absent among the Anga, and to have an incidence of 11% on Loh, 17% on Merig, 34% on Ifaluk, and 55% on Anuta. Data on the prevalence of tuberculous infection obtained by skin tests reflected the reported prevalence of symptomatic tuberculosis in all groups. The frequency of reactions to 0.0001 mg doses of the atypical mycobacterial antigens corresponded to tuberculin sensitivity in the different groups: none among the Anga, sporadic on Loh and Merig, and common on Ifaluk and Anuta. However, analysis of PPD profiles suggests that actions greater than or equal to 5 mm to a 0.1 ml dose of 1:100 coccidioidin were observed in 26% of the population of Ifaluk, and of 1:100 histoplasmin in 8% of the population of Anuta, and 14-16% of the populations of the two New Guinean villages.

Reproductive effort and life history strategy of the Aldabran giant tortoise

THE Aldabra giant tortoise, Geochelone gigantea Schweigger, has a large body size (19–120 kg)1, long life span (65–90 yr)2, late maturity (females 17–23 yr)3,4 and iteroparity3. The three isolated island populations of different densities on Aldabra show dissimilarity in their reproductive parameters (for example mean clutch size, mean egg weight, proportion of mature females breeding and the number of clutches per female per year) and in the variation of these parameters from year to year through annual changes in rainfall3. Moreover, their reproductive response to these changes in rainfall is rapid; they have a relatively high maximum (potential) rate of natural increase (maximum clutch size 28)3 and mature females in the high density population are half the weight of those in the low density area2,4. I have postulated that the reproductive effort would differ between the different density populations and that this effort would change in relation to changes in food availability. This contention is supported by the results reported here.

Retrospective studies on the twinning rate in Scandinavia.

The rates of human multiple maternities in the Nordic countries were studied from continuous series of data. In the Åland and Åboland archipelagos the parish records for births and baptisms since the 1650's were used. Various sources, some unpublished, in the archives of statistics were used for Sweden (since 1749) and Finland (since 1859) as a whole. Until recently, the rates of multizygotic multiple maternities in isolated island populations in the Åland and Åboland archipelagos have been some of the highest known among Whites (15-20‰). Highly significant temporal fluctuations in the twinning rates were noted. In Sweden, the twinning rate during the last part of 18th century was about twice as high as it was in 1966-70. The triplet and quadruplet rates were about three to four times as high as they are nowadays. There has been a secular decline in DZ twinning. This downward trend set in first in the isolated populations. In Sweden, it started in the 1930's, but in Finland, not until the 1960's. The steep downward trend in the twinning rates is shown to set in about one generation after the break-up of isolation. This can be interpreted as evidence that the changes in matrimonial migration patterns have affected the rates of DZ twinning.

Enzyme gene heterozygosity in small island populations of Philaenus spumarius (L.) (Homoptera)

Genetic polymorphism at about twenty enzyme loci in one mainland and in six differentially isolated island populations of Philaenus spumarius (L.) was studied by starch gel electrophoresis. The populations have different average degrees of heterozygosity, so that the most isolated population is the least polymorphic. The differences in heterozygosity seem to be correlated to the size of the population and the degree of isolation from other populations. With a single exception, the most common allele in each locus is the most common one everywhere. The results are compared with the differences observed in the color polymorphism of Philaenus island populations. The allele frequencies of enzyme loci are maintained by selection; the fact that the prevalent allele is the same in all populations may be due to selection and founder principle.

GENETIC STUDIES OF IRRADIATED NATURAL POPULATIONS OF DROSOPHILA. II. 1957 TESTS

BS>Genetic analyses were made of irradiated and control isolated populations of D. ananassae from the Pacific Proving Ground area, others of the Marshall Islands, and Ponape. These tests shows that the Bikini and Rongelap populations were severely damaged genetically by the direct radiations and fallout from the thermonuclear device exploded on March 1, 1954. The Rongerik atoll populations had recovered from fallout by August 1955 -- a period roughly equivalent to 26 generations. The populations collected at Rongelap and Bikini had not recovered then, but the Rongelap populatlon had recovered by 1956, in 40 or more generations. Because of the heavier irradiation on Bikini--including effects of the weapons tests in 1956--this population was still slightly below other Pacific Island populations even in 1957. The general relations and comparisons between these isolated island populations and other Drosophila- populations are discussed. (auth)