Joint evolution of altruistic cooperation and dispersal in a metapopulation of small local populations

We investigate the joint evolution of public goods cooperation and dispersal in a metapopulation model with small local populations. Altruistic cooperation can evolve due to assortment and kin selection, and dispersal can evolve because of demographic stochasticity, catastrophes and kin selection. Metapopulation structures resulting in assortment have been shown to make selection for cooperation possible. But how does dispersal affect cooperation and vice versa, when both are allowed to evolve as continuous traits? We found four qualitatively different evolutionary outcomes. (1) Monomorphic evolution to full defection with positive dispersal. (2) Monomorphic evolution to an evolutionarily stable state with positive cooperation and dispersal. In this case, parameter changes selecting for increased cooperation typically also select for increased dispersal. (3) Evolutionary branching can result in the evolutionarily stable coexistence of defectors and cooperators. Although defectors could be expected to disperse more than cooperators, here we show that also the opposite case is possible: Defectors tend to disperse less than cooperators when the total amount of cooperation in the dimorphic population is low enough. (4) Selection for too low cooperation can cause the extinction of the evolving population. For moderate catastrophe rates dispersal needs to be initially very frequent for evolutionary suicide to occur. Although selection for less dispersal in principle could prevent such evolutionary suicide, in most cases this rescuing effect is not sufficient, because selection in the cooperation trait is typically much stronger. If the catastrophe rate is large enough, a part of the boundary of viability can be evolutionarily attracting with respect to both strategy components, in which case evolutionary suicide is expected from all initial conditions

Metapopulation dynamics and the evolution of sperm parasitism

Amazon molly (Poecilia formosa) females reproduce asexually, but they need sperm to initiate the process. Such gynogenetic reproduction can be called sperm parasitism since the DNA in the sperm is not used. Since all offspring of asexually reproducing females are females, they can locally outcompete sexually reproducing ones, but their persistence is threatened by the lack of males. Therefore, the existence of Amazon mollies is puzzling. A metapopulation structure has been suggested to enable the coexistence of gynogenetic and sexual species. Previously only Levins-type metapopulation models have been used to investigate this question, but they are not defined on the individual level. Therefore we investigate the evolution of sperm parasitism in a structured metapopulation model, which incorporates both realistic local population dynamics and individual-level dispersal. If the reproduction strategy is freely evolving in a large well-mixed population or in the structured metapopulation model, strong discrimination of asexually reproducing females by males results in evolution to full sexuality, whereas mild discrimination leads to too small probability of sexual reproduction, so that the lack of males causes the extinction of the evolving population, resulting in evolutionary suicide. This classification remains the same also when both sexual reproduction and dispersal are freely evolving. Sexual and asexual behaviour can be observed at the same time in this model in the presence of a trade-off between the reproduction and dispersal traits. However, we do not observe disruptive selection resulting in the evolutionarily stable coexistence of fully sexual and fully asexual females. Instead, the presence of sexual and asexual behaviour is due to females with a mixed reproduction trait.</p

The Effects of the Breast Cancer Mammography Screening Programme in Women aged 40 to 84 years in Turku, Finland (1987-2009)

The objective of this thesis was to evaluate whether a more extensive mammography screening programme (TurkuMSP) conducted by the city of Turku, had an effect on breast cancer (BC) incidence, survival, or mortality in years 1987 to 2009. Despite the fact that some studies have suggested a 20 percent reduction in BC mortality due to mammography screening, there are findings of harm to subjects, which are claimed to negate the benefits of screening. Thus, the aims of this study are most pertinent. A total of 176 908 screening examinations were performed in 36 000 women aged 40−74 during the years 1987−1997. In all, 685 primary BCs were found in the screened women, either screen-detected (n=531) or during screening intervals (n=154). Survival and BC recurrence rate of women with screen-detected BC was compared to 184 women with clinical BCs detected among individuals who did not take part in the screening. The invitation interval, which may influence the outcome, was studied in the age group 40 to 49 by inviting those born in even calendar years annually for mammography screening and those born in odd years, triennially. In addition, BC incidence and mortality in the total female population of Turku aged 40 to 84 years was compared with the respective figures of Helsinki and the rest of Finland, both during the pre-screening era (1976-1986) and the screening era (1987-2009). The study was designed to compare women by age groups, because women aged 50 to 59 were generally screened in all of Finland, whereas only in Turku women aged 40 to 49 and 60 to 74 were screened in addition. Data regarding cancer recurrence were derived from the Finnish Cancer Registry and data on deaths were collected from Statistics Finland. In survival analyses, screened women with invasive BC had a significantly higher survival rate than the women with clinical BC. The survival benefit started to appear already during the first follow-up years and was evident in all age groups. A marginal survival extension was also seen in screened women when BC had spread to ipsilateral axillary nodes already at diagnosis. Recurrence-free survival rate after BC treatment was significantly more favorable among the screened women compared with women with BC found clinically. The screening invitation interval did not significantly influence BC mortality in the subset of women aged 40 to 49 years. There were no consistent differences in the changes of BC incidence between Turku and the comparison areas during the screening era. In Turku, the BC mortality incidence in women aged 55−69 years was significantly lower during the screening era (from 1987 to 1997) compared with the pre-screening era, whereas no such change was found in the city of Helsinki or Tampere. When comparing the changes in incidence-based BC mortality during years 1987 to 2009 in Turku to those of Helsinki and the rest of Finland, there was a suggestion of more than 20 percent lower mortality in Turku among oldest age group (75-84 years) compared with the reference residential areas, but the differences were not consistently significant. Interpretation of the study results should be made with caution because there were no random control groups, and on the other hand, the number of cases in subgroups was fairly low to yield definite conclusions. Also due to the many statistical analyses, some of the findings may be due to chance. The results are, however, suggestive for a decrease of BC mortality in the elderly age groups due to wide mammography screening. This finding needs confirmation in further studies before recommending an expansion of mammography screening to women up to the age of 74 yearsTurun Mammografiaseulontaohjelman vaikutukset 40-84 -vuotiaisiin turkulaisnaisiin (1987-2009) Tämän väitöskirjatyön tarkoituksena oli selvittää, voitiinko tavanomaista laajemmalla, Turussa toteutetulla mammografiaseulontaohjelmalla (TurunMSP-ohjelma) vaikuttaa rintasyövän ilmaantuvuuteen, eloonjäämiseen tai kuolleisuuteen vuosien 1987-2009 välisenä aikana. Vaikka jotkut tutkimukset ovat osoittaneet 20 %:n suuruusluokkaa olevia rintasyöpäkuolleisuuden vähenemiä mammografiaseulontojen tuloksena, on myös esitetty tutkimustuloksia, joissa seulontaohjelmiin liittyvät haitat kumoavat seulonnalla saadut hyödyt. Näin ollen tämän tutkimuksen tavoitteita voidaan pitää edelleen ajankohtaisina. Kun 176 908 seulontatutkimusta tehtiin Turussa 36 000:lle 40-74-vuotiaalle naiselle vuosina 1987-1997, löydettiin heiltä 685 primaarisyöpää, joko seulonnan yhteydessä (n = 531) tai välisyöpinä (n = 154). Näiden tapausten eloonjäämistä ja rintasyövän uusiutumista verrattiin seulonnan ulkopuolella kliinisesti havaittuihin 184 rintasyöpään. Koska seulontakutsun aikaväli saattaa vaikuttaa seulonnan tuloksiin, tutkittiin tätä asiaa 40-49-vuotiaiden naisten ikäryhmässä, kutsumalla parillisina kalenterivuosina syntyneet naiset mammografiaseulontaan vuosittain ja parittomina vuosina syntyneet joka kolmas vuosi. Tämän lisäksi Turun tuloksia verrattiin 40-84-vuotiaiden naisten osalta Helsingin ja muun Suomen tuloksiin sekä seulontaa edeltäneellä ajanjaksolla (1976-86) että seulontajaksolla (1987-2009). Tutkimus suoritettiin ikäryhmittäisenä vertailuna, koska Suomessa seulottiin tuolloin yleensä vain 50-59-vuotiaat naiset, kun sen sijaan vain Turussa myös 40-49-vuotiaat ja 60-74-vuotiaat. Syöpätapauksia koskevat tilastotiedot hankittiin Suomen Syöpärekisteristä ja kuolleisuustiedot Tilastokeskukselta. Invasiivisten rintasyöpätapausten eloonjäämistulokset olivat seulotuilla naisilla merkitsevästi paremmat kuin kliinisesti diagnostisoiduilla naisilla. Eloonjäämishyötyä alkoi näkyä jo ensimmäisistä seurantavuosista alkaen, ja se näkyi kaikissa ikäryhmissä. Marginaalinen eloonjäämishyöty havaittiin myös niillä naisilla, joiden syöpä oli ehtinyt levitä kainalon seutuun diagnoosihetkellä. Myös taudin uusiutumiseen kuluva aika oli rintasyöpähoidon saamisen jälkeen merkitsevästi pidempi seulonnassa löytyneiden tautitapausten osalta verrattuna kliinisesti löytyneisiin tapauksiin. Kutsumistiheyden eroilla ei näyttänyt olevan vaikutusta (40-49-vuotiailla). Turun naisten rintasyövän ilmaantuvuuden muutoksissa ei havaittu eroja vertailualueiden ilmaantuvuuden muutoksiin verrattuna mammografiaohjelman seulontajakson aikana. 55-69-vuotiaiden naisten rintasyöpäkuolleisuus oli Turussa merkittävästi pienempi seulontajaksolla (1987-1997) kuin sitä edeltäneellä jaksolla, jolloin seulontaohjelmat eivät vielä olleet käynnistyneet. Vastaavaa muutosta ei Helsingissä tai Tampereella havaittu. Kun vertailtiin puolestaan Turussa tapahtuneiden ilmaantuvuusperusteiseen rintasyöpäkuolleisuuden muutoksia vuosina 1987-2009 Helsingissä ja muualla Suomessa tapahtuneisiin muutoksiin, saatiin selviä viitteitä iäkkäimmän naisryhmän yli 20 % vertailualueita suuremmasta rintasyöpäkuolleisuuden pienentymisestä (75-84-vuotiaat), mutta tulokset eivät olleet kaikilta osin johdonmukaisesti merkitseviä. Tämän tutkimuksen tulosten johtopäätökset on tehtävä varoen, sillä tutkimus ei toisaalta sisältänyt satunnaistettuja kokeita, ja toisaalta tapausten määrä oli joissakin alaryhmissä melko alhainen sitovien päätelmien tekemiseksi. Koska tutkimuskokonaisuuden aikana käytettiin useita erilaisia laskentamenetelmiä, jotkut tutkimuksen tulokset voivat myös johtua sattumasta. Tulokset kuitenkin viittaavat siihen, että varsinkin iäkkäimmissä naisryhmissä havaittu rintasyöpäkuolleisuuden lasku johtui laajasta mammografiaseulonnasta. Tämä havainto edellyttää kuitenkin vielä jatkotutkimusten kautta hankittavaa lisänäyttöä ennen kuin voidaan suositella seulontaohjelman laajentamista 74-vuoden ikään asti.Siirretty Doriast

Self-extinction through optimizing selection

Evolutionary suicide is a process in which selection drives a viable population to extinction. So far such selection-driven self-extinction has been demonstrated in models with frequency-dependent selection. This is not surprising, since frequency-dependent selection can disconnect individual-level and population-level interests through environmental feedback. Hence it can lead to situations akin to the tragedy of the commons, with adaptations that serve the selfish interests of individuals ultimately ruining a population. For frequency-dependent selection to play such a role, it must not be optimizing. Together, all published studies of evolutionary suicide have created the impression that evolutionary suicide is not possible with optimizing selection. Here we disprove this misconception by presenting and analyzing an example in which optimizing selection causes self-extinction. We then take this line of argument one step further by showing, in a further example, that selection-driven self-extinction can occur even under frequency-independent selection

Evolution of site-selection stabilizes population dynamics, promotes even distribution of individuals, and occasionally causes evolutionary suicide

Species that compete for access to or use of sites, such as parasitic mites attaching to honey bees or apple maggots laying eggs in fruits, can potentially increase their fitness by carefully selecting sites at which they face little or no competition. Here, we systematically investigate the evolution of site-selection strategies among animals competing for discrete sites. By developing and analyzing a mechanistic and population-dynamical model of site selection in which searching individuals encounter sites sequentially and can choose to accept or continue to search based on how many conspecifics are already there, we give a complete characterization of the different site-selection strategies that can evolve. We find that evolution of site-selection stabilizes population dynamics, promotes even distribution of individuals among sites, and occasionally causes evolutionary suicide. We also discuss the broader implications of our findings and propose how they can be reconciled with an earlier study (Nonaka et al. in J Theor Biol 317:96–104, 2013) that reported selection toward ever higher levels of aggregation among sites as a consequence of site-selection

On Diploid versus Clonal ESSes in Metapopulations

Most studies of evolutionary stable strategies (ESSes) assume clonal reproduction. At least in the simplest cases, more realistic genetic models yield results compatible with the clonal results. In this paper we study a case where the diploid and clonal results are not expected to be similar: evolution in a metapopulation with small local population sizes. It turns out, that although there are differences between the clonal and diploid ESS dispersal rates, the trait under consideration, the discrepancy is irrelevant for all practical purposes (less than 2%)

Introduction to Gamification Minitrack

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Evolutionary Suicide and Evolution of Dispersal in Structured Metapopulations

In this article we study the evolution of dispersal in a structured metapopulation model. The metapopulation consists of a large (infinite)number of local populations living in patches of habitable environment. Dispersal between patches is modeled by a disperser pool and individuals in transit between patches are exposed to a risk of mortality. Occasionally, local catastrophes eradicate a local population: all individuals in the affected patch die, yet the patch remains habitable. The rate at which such disasters occur can depend on the local population size of a patch. We prove that, in the absence of catastrophes, the strategy not to migrate is evolutionarily stable. It is also convergence stable unless there is no mortality during dispersal. Under a given set of environmental conditions, a metapopulation may be viable and yet selection may favor dispersal rates that drive the metapopulation to extinction. This phenomenon is known as evolutionary suicide. We show that in our model evolutionary suicide can occur for certain types of size-dependent catastrophes. Evolutionary suicide can also happen for constant catastrophe rates, if local growth within patches shows an Allee effect. We study the evolutionary bifurcation towards evolutionary suicide and show that a discontinuous transition to extinction is a necessary condition for evolutionary suicide to occur. In other words, if population size smoothly approaches zero at a boundary of viability in parameter space, this boundary is evolutionarily repelling and no suicide can occur