Where Two Are Fighting, the Third Wins: Stronger Selection Facilitates Greater Polymorphism in Traits Conferring Competition-Dispersal Tradeoffs

A major conundrum in evolution is that, despite natural selection, polymorphism is still omnipresent in nature: Numerous species exhibit multiple morphs, namely several abundant values of an important trait. Polymorphism is particularly prevalent in asymmetric traits, which are beneficial to their carrier in disruptive competitive interference but at the same time bear disadvantages in other aspects, such as greater mortality or lower fecundity. Here we focus on asymmetric traits in which a better competitor disperses fewer offspring in the absence of competition. We report a general pattern in which polymorphic populations emerge when disruptive selection increases: The stronger the selection, the greater the number of morphs that evolve. This pattern is general and is insensitive to the form of the fitness function. The pattern is somewhat counterintuitive since directional selection is excepted to sharpen the trait distribution and thereby reduce its diversity (but note that similar patterns were suggested in studies that demonstrated increased biodiversity as local selection increases in ecological communities). We explain the underlying mechanism in which stronger selection drives the population towards more competitive values of the trait, which in turn reduces the population density, thereby enabling lesser competitors to stably persist with reduced need to directly compete. Thus, we believe that the pattern is more general and may apply to asymmetric traits more broadly. This robust pattern suggests a comparative, unified explanation to a variety of polymorphic traits in nature.ope

Neuropathological Findings In Chronic Relapsing Experimental Allergic Neuritis Induced In The Lewis Rat By Inoculation With Intradural Root Myelin And Treatment With Low Dose Cyclosporin A

Experimental allergic neuritis (EAN) was induced in Lewis rats by inoculation with bovine intradural root myelin and adjuvants. Rats treated with subcutaneous cyclosporin A (CsA) (4mg/kg on 3 days per week from the day of inoculation until day 29) developed a chronic relapsing course. Tissues from the spinal cord, nerve roots, dorsal root ganglia and sciatic nerve of CsA-treated rats sampled during relapses and remissions were studied during or after episodes of acute EAN. Both control and CsA-treated animals studied in the first episode of EAN had evidence of inflammation and primary demyelination of the nerve roots and dorsal root ganglia. In control and CsA-treated animals in the second episode there was severe inflammation and demyelination and remyelination in the spinal nerves and sciatic nerves and dorsal columns of the spinal cord, particularly in later stages of the disease. In later episodes there was less inflammation, but there was continuing demyelination and onion bulbs were present. In animals sampled after recovery from chronic relapsing EAN onion bulbs were present. Occasional small onion bulbs were also observed in control animals that were inoculated with higher doses of myelin. Plasma cells were present in the inflammatory lesions of later episodes. Mast cells were also observed at different stages of the disease. We conclude that the CsA form of chronic relapsing EAN has clinical and pathological similarities with the human disease, chronic inflammatory demyelinating polyradiculoneuropathy

Strong differences in the clonal variation of two Daphnia species from mountain lakes affected by overwintering strategy

<p>Abstract</p> <p>Background</p> <p>The population structure of cyclical parthenogens such as water fleas is strongly influenced by the frequency of alternations between sexual and asexual (parthenogenetic) reproduction, which may differ among populations and species. We studied genetic variation within six populations of two closely related species of water fleas of the genus <it>Daphnia </it>(Crustacea, Cladocera). <it>D. galeata </it>and <it>D. longispina </it>both occur in lakes in the Tatra Mountains (Central Europe), but their populations show distinct life history strategies in that region. In three studied lakes inhabited by <it>D. galeata</it>, daphnids overwinter under the ice as adult females. In contrast, in lakes inhabited by <it>D. longispina</it>, populations apparently disappear from the water column and overwinter as dormant eggs in lake sediments. We investigated to what extent these different strategies lead to differences in the clonal composition of late summer populations.</p> <p>Results</p> <p>Analysis of genetic variation at nine microsatellite loci revealed that clonal richness (expressed as the proportion of different multilocus genotypes, MLGs, in the whole analysed sample) consistently differed between the two studied species. In the three <it>D. longispina </it>populations, very high clonal richness was found (MLG/N ranging from 0.97 to 1.00), whereas in <it>D. galeata </it>it was much lower (0.05 to 0.50). The dominant MLGs in all <it>D. galeata </it>populations were heterozygous at five or more loci, suggesting that such individuals all represented the same clonal lineages rather than insufficiently resolved groups of different clones.</p> <p>Conclusions</p> <p>The low clonal diversities and significant deviations from Hardy-Weinberg equilibrium in <it>D. galeata </it>populations were likely a consequence of strong clonal erosion over extended periods of time (several years or even decades) and the limited influence of sexual reproduction. Our data reveal that populations of closely related <it>Daphnia </it>species living in relatively similar habitats (permanent, oligotrophic mountain lakes) within the same region may show strikingly different genetic structures, which most likely depend on their reproductive strategy during unfavourable periods. We assume that similar impacts of life history on population structures are also relevant for other cyclical parthenogen groups. In extreme cases, prolonged clonal erosion may result in the dominance of a single clone within a population, which might limit its microevolutionary potential if selection pressures suddenly change.</p

PRECATIO || AD CHRI=||STVM,|| PRO CALAMITATVM || vbi[que] ingruentium mitiga-tione,|| AB || ADAMO LAMPERTO || Seruestensi scripta & filijs suis || dedicata.||

Vorlageform des Erscheinungsvermerks: VVITEBERGAE || TYPIS CLEMENTIS || SCHLEICH.|| (M.D.LXXIX.||?

Illustration of the three cases that we consider.

(A) Case 1: Both countries have the same population size and infection level. (B) Case 2: Both countries have the same population size, but country 1 has a more severe outbreak. (C) Case 3: One U.S. state is a “hotspot” and has a more severe outbreak than the rest of the U.S.</p

DE SATANA || GENERIS || HVMANI HO-||STE FEROCIS=||SIMO || DIALOGVS,|| Pio studio scriptus, & in lu-||cem recens editus || Ab || ADAMO LAMPERTO || SERVESTENSI.||

Vorlageform des Erscheinungsvermerks: VVITEBERGAE || Typis Clementis Schleich et An-||tonij Schön.|| M.D.LXXVIII.|

The equilibrium solution dictates that governments release the quarantines earlier than optimal.

We consider the three cases illustrated in Fig 1: identical countries (A, B), non-identical countries (C, D), and a state that initially has a much higher infection level than the rest of the U.S. (E, F). The left column (A, C, E) shows the optimal time for country 1 to release its quarantine, , as a function of the time when country 2 releases its quarantine, T2 (blue line). It also shows the optimal time for country 2 to release its quarantine, , as a function of the time when country 1 releases its quarantine, T1, on a flipped axis (mirror image, red line). The intersection of the blue and the red line indicates the open-loop Nash equilibrium. Note that a unique Nash equilibrium exists for each of the three demonstrated cases. For comparison, the purple dots show the socially optimal solution. In turn, the right column (B, D, E) shows the time evolution of the infection level in countries 1 and 2, assuming that they adopt the Nash equilibrium strategies (, blue line, and , red line), as well as the infection levels assuming that the countries adopt the socially optimal solution (, light blue line, and , light red line). In all three cases, the governments release the quarantine sooner than the optimum if they follow the Nash equilibrium. Note that in both the socially optimal solution and the Nash equilibrium, the actions of both governments tend to be synchronized: The second country that switches to a non-restrictive quarantine does so approximately when its infection level approaches that of the first country. Parameters: (all panels) r0 = −5% (day−1), Imax = 0.1 (% of population), Imin = 0.005 (% of population), Tdelay = 14 (days); (A, B) r1 = r2 = 7% (day−1), N1 = N2 = 1, μ12 = μ21 = 0.2%; (C, D) r1 = 9% (day−1), r2 = 7% (day−1), N1 = N2 = 1, μ12 = μ21 = 0.25%; (E, F) r1 =11% (day−1), r2 = 5% (day−1), N1 = 0.3, N2 = 1, μ12 = 0.25%×N1, μ21 = 0.25%×N2.</p

Precatio || AD CHRISTVM || PRO REMISSIONE || PECCATORVM,|| Scripta in gratiam & hono=||rem Clarissimi Viri, Iuris vtrius[que] Doctoris || Marci Zimmerman, inclyti Principatus || Anhaltini Consiliarij, & amplissimi Se=||natus Augustani Syndici, &c.|| Domini sui perpetuo || colendi,|| ab || Adamo Lamperto || ciue Seruestensi.||

Vorlageform des Erscheinungsvermerks: LIPSIAE || Iohannes Rhamba excudebat || M.D.LXX[?] |