The retinotectofugal system is the main visual pathway projecting upon the telencephalon in birds and many other nonmammalian vertebrates. The ascending tectal projection arises exclusively from cells located in layer 13 of the optic tectum and is directed bilaterally toward the thalamic nucleus rotundus. Although previous studies provided evidence that different types of tectal layer 13 cells project to different subdivisions in Rt, apparently without maintaining a retinotopic organization, the detailed spatial organization of this projection remains obscure. We reexamined the pigeon tectorotundal projection using conventional tracing techniques plus a new method devised to perform small deep-brain microinjections of crystalline tracers. We found that discrete injections involving restricted zones within one subdivision retrogradely label a small fraction of layer 13 cells that are distributed throughout the layer, covering most of the tectal representation of the contralateral visual field. Double-tracer injections in one subdivision label distinct but intermingled sets of layer 13 neurons. These results, together with the tracing of tectal axonal terminal fields in the rotundus, lead us to propose a novel "interdigitating" topographic arrangement for the tectorotundal projection, in which intermingled sets of layer 13 cells, presumably of the same particular class and distributed in an organized fashion throughout the surface of the tectum, terminate in separate regions within one subdivision. This spatial organization has significant consequences for the understanding of the physiological and functional properties of the tectofugal pathway in birds.

1. The extent to which flower colour and other visual cues influence butterfly flower choice in the field is poorly understood, especially in comparison with choices by Hymenoptera.2. Using a novel approach to studies of visitation behaviour by butterflies, flower colour of four Asteraceae species was phenotypically manipulated to decouple the influence of that trait from others (including morphology and nectar rewards) on visitation by Lycaena heteronea, Speyeria mormonia, Cercyonis oetus, and Phyciodes campestris.3. Flower visits were recorded to experimental flower arrays in subalpine meadows to measure (i) spontaneous preference by butterflies for particular colours and other traits and (ii) flower constancy (longer than expected strings of visits made to flowers of the same species), a behaviour that can reduce interspecific gene flow in plants.4. Over three field seasons, 3558 individual flower visits in 1386 foraging bouts were observed for free-flying butterflies. All four butterfly species responded to the phenotypic manipulations of flower colour, although in different ways. Speyeria mormonia and L. heteronea also exhibited preferences based on other flower traits. Lycaena heteronea responded to combinations of traits such that the other traits it preferred depended upon the context of flower colour.5. None of the butterfly species exhibited flower constancy in any of the arrays employed.6. The observed preferences show that butterflies, like some other pollinators, are potentially capable of exerting selection on colour and other floral traits. Moreover, these flower preferences can depend on the context of other flower traits. The absence of constancy contrasts with reports of high constancy in many bees.

We describe the geographical variation of corolla and nectar guide size in seven populations of Mimulus luteus (Phrymaceae) in central Chile, and examine whether flower phenotypes associate with taxonomic composition and flower visit patterns of pollinators across populations. Flowers showed higher variation in nectar guide size than corolla size. Mean corolla size increased with the proportion of bees and decreased with the proportion of lepidopterans in the pollinator assemblages. Nectar guide size increased with the proportion of hummingbirds in the pollinator assemblages. When the frequency of flower visits rather than taxonomic composition was considered, the results revealed similar patterns. Because these traits previously have been described as targets of bee‐ and hummingbird‐mediated selection in M. luteus, our results have implications for understanding the processes that determine flower diversification in Chilean Mimulus. Although we cannot rule out ecological sorting as an explanation for the geographical association between pollinators and flower phenotypes, changes in the prevalence and importance of bees and hummingbirds across populations appear to account, at least in part, for the flower phenotypic variation across populations. The extent to which insect and hummingbird pollination in M. luteus produces pollinator‐mediated divergence among populations needs to be examined in future studies.

Background: The increase in availability of genomic sequences for a wide range of organisms has revealed gene duplication to be a relatively common event. Encounters with duplicate gene copies have consequently become almost inevitable in the context of collecting gene sequences for inferring species trees. Here we examine the effect of incorporating duplicate gene copies evolving at different rates on tree reconstruction and time estimation of recent and deep divergences in butterflies.