Utilization of molecular phylogenetic information over the past decade has resulted in clarification of the position of most angiosperms. In contrast, the position of the holoparasitic family Hydnoraceae has remained controversial. To address the question of phylogenetic position of Hydnoraceae among angiosperms, nuclear SSU and LSU rDNA and mitochondrial atp1 and matR sequences were obtained for Hydnora and Prosopanche. These sequences were used in combined analyses that included the above four genes as well as chloroplast rbcL and atpB (these plastid genes are missing in Hydnoraceae and were hence coded as missing). Three data sets were analyzed using maximum parsimony: (1) three genes with 461 taxa; (2) five genes with 77 taxa; and (3) six genes with 38 taxa. Analyses of separate and combined data partitions support the monophyly of Hydnoraceae and the association of that clade with Aristolochiaceae sensu lato (s.l.) (including Lactoridaceae). The latter clade is sister to Piperaceae and Saururaceae. Despite over 11 kilobases (kb) of sequence data, relationships within Aristolochiaceae s.l. remain unresolved, thus it cannot yet be determined whether Aristolochiaceae, Hydnoraceae, and Lactoridaceae should be classified as distinct families. In contrast to most traditional classifications, molecular phylogenetic analyses do not suggest a close relationship between Hydnoraceae and Rafflesiaceae. A number of morphological features is shared by Hydnoraceae and Aristolochiaceae; however, a more resolved phylogeny is required to determine whether these represent synapomorphies or independent acquisitions.

Large flowers often contain larger nectar rewards, and receive more pollinator visits, than small flowers. We studied possible behavioral mechanisms underlying the formation of flower size preferences in bumblebees, using a two‐phase laboratory experiment. Experimentally naive Bombus terrestris (L.) foraged on artificial flowers that bore either a large (3.8 cm diameter) or a small (2.7 cm diameter) display of a uniform color. Only flowers of one display size contained nectar rewards. We changed the display color and the locations of large and small flowers in the second experimental phase. We recorded the bees' choices in both phases. Almost half of the bees (41%) made their first visit to a small flower. The bees learned to associate display size with food reward, and chose rewarding flowers with >85% accuracy by the end of each experimental phase. Some learning occurred within the bees' first three flower visits. Learning of the size–reward association was equally good for large and small displays in the first experimental phase, but better for small displays in the second phase. Formation of size–reward associations followed a similar course in both phases. This suggests that the bees did not apply their experience from the first learning phase to the new situation of the second phase. Rather, they treated each phase of the experiment as an independent learning task. Our results suggest that associative learning is involved in the formation of preferences for large displays by bees. Moreover, bees that had learned to prefer large displays in one foraging situation may not transfer this preference to a novel situation that is sufficiently different. We propose that this feature of the bees' behavior can select for honest advertising in flowers.

Background: The phylogenetic relationships among the holoparasites of Rafflesiales have remained enigmatic for over a century. Recent molecular phylogenetic studies using the mitochondrial matR gene placed Rafflesia, Rhizanthes and Sapria (Rafflesiaceae s. str.) in the angiosperm order Malpighiales and Mitrastema (Mitrastemonaceae) in Ericales. These phylogenetic studies did not, however, sample two additional groups traditionally classified within Rafflesiales (Apodantheaceae and Cytinaceae). Here we provide molecular phylogenetic evidence using DNA sequence data from mitochondrial and nuclear genes for representatives of all genera in Rafflesiales.

Comparative studies on floral morphology, anatomy, and histology were performed to identify shared features of the genera of Apodanthaceae (Rafflesiales): Apodanthes, Pilostyles, and Berlinianche. Berlinianche was studied for the first time in detail and its affinity to Apodanthaceae was confirmed. It has a previously undescribed hair cushion on the inner perianth organs and inaperturate pollen. Shared features of members of Apodanthaceae are: unisexual flowers; three (or four) alternating di-/tetra-or tri-/hexamerous whorls of scales of which the inner one or two correspond to a perianth; a synandrium with pollen sacs typically arranged in two rings; opening by a dehiscence line between the two rings of pollen sacs; large vesicular hairs above the synandrium; a gynoecium with four united carpels; inferior and unilocular ovaries with four parietal placentae, ovules tenuinucellate, anatropous with two well developed integuments, oriented in various directions; a nectary disk. Apodanthaceae share some special structural features with Malvales

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A basic evolutionary problem posed by the Iterated Prisoner's Dilemma game is to understand when the paradigmatic cooperative strategy Tit-for-Tat can invade a population of pure defectors. Deterministically, this is impossible. We consider the role of demographic stochasticity by embedding the Iterated Prisoner's Dilemma into a population dynamic framework. Tit-for-Tat can invade a population of defectors when their dynamics exhibit short episodes of high population densities with subsequent crashes and long low density periods with strong genetic drift. Such dynamics tend to have reddened power spectra and temporal distributions of population size that are asymmetric and skewed toward low densities. The results indicate that ecological dynamics are important for evolutionary shifts between adaptive peaks. The Prisoner's Dilemma game contains the basic paradox for the evolution of reciprocal altruism (1, 2). In this game, each of two players can either cooperate or defect. This leads to four possible payoffs S Ͻ P Ͻ R Ͻ T: if one player cooperates and the other defects, the cooperator gets S and the defector gets T, if both players cooperate they both get R, and if both defect they get P. No matter what the other does, it is always best to defect (R Ͻ T and S Ͻ P), but if both would cooperate they would both receive a higher payoff than if both defect (P Ͻ R). If payoffs are interpreted as Darwinian fitness, this game exemplifies the advantage of selfish mutants and the evolution of maladaptive noncooperative behavior. The paradox has a solution in the Iterated Prisoner's Dilemma (1), in which opponents meet again with a certain probability. In this new game, the Tit-for-Tat (TFT) strategy-cooperate in the first round, then do whatever the opponent did in the previous round-does very well against a wide variety of other strategies (3). TFT captures the essence of reciprocal altruism (4), and once established, TFT can catalyze the evolution of even more cooperative strategies (5, 6). Thus, TFT represents a cornerstone in the evolution of cooperation, and it is important to determine the conditions under which TFT can evolve in a population of pure defectors.We consider the evolutionary game between the strategies TFT and AD-always defect, regardless of the opponent's decisions-in the Iterated Prisoner's Dilemma. Let w be the probability that opponents meet again. Then the payoffs between TFT and AD are as shown in Table 1, in which the entries are the payoffs received by the strategy in the left column when playing against the strategy in the top row. For example, when TFT plays against AD, it gets S in the first round and P in all successive rounds, hence a total of S ϩ wP ϩ w 2 P ϩ . . . . AD gets T in the first round and P thereafter. Thus the payoff for TFT is S ϩ wP͞(1 Ϫ w), whereas that of AD is T ϩ wP͞(1 Ϫ w). The other payoffs are calculated similarly. In a population consisting of a mixture of TFT and AD, the payoffs of the two strategies depend on their frequencies. If p is the frequency of TFT...

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