Coevolutionary Changes Research Articles

Molecular variability in Amerindians: widespread but uneven information.

A review was made in relation to the molecular variability present in North, Central, and South American Indian populations. It involved results from ancient DNA, mitochondrial DNA in extant populations, HLA and other autosomal markers, X and Y chromosome variation, as well as data from parasitic viruses which could show coevolutionary changes. The questions considered were their origin, ways in which the early colonization of the continent took place, types and levels of the variability which developed, peculiarities of the Amerindian evolutionary processes, and eventual genetic heterogeneity which evolved in different geographical areas. Although much information is already available, it is highly heterogeneous in relation to populations and types of genetic systems investigated. Unfortunately, the present trend of favoring essentially applied research suggest that the situation will not basically improve in the future.

The evolution of thunniform locomotion and heat conservation in scombrid fishes: New insights based on the morphology ofAllothunnus fallai

Two significant functional differences—a more anterior and internally positioned red myoÍtomal muscle mass and modification of the red-muscle vascular supply to form counter-current heat exchangers—distinguish the tunas (tribe Thunnini) from other species in the teleost family Scombridae. Neither of these characteristics is found in the bonitos (tribe Sardini), the sister group to the Thunnini. The most recent scombrid classification places the slender tuna, Allothunnus fallai, in the tribe Sardini, but some earlier studies suggested that this species should be a member of the Thunnini. Allothunnus fallai does not possess the lateral subcutaneous arteries and veins or the lateral heat-exchanging retia typical of tunas. However, we have found that this species has a highly modified central circulation (dorsal aorta, post cardinal vein, and associated branch vessels) similar to the central heat-exchanging retia of certain tunas, an enlarged haemal arch to accommodate this structure, and the anterior, internal placement of red muscle characteristic of tunas. With these new characters, phylogenetic reconstructions based on parsimony place A. fallai as the sister taxon to the tunas, establish that it is the most basal tuna species, and support the hypothesis that the derivation of tunas from a bonito-like ancestor occurred through selection for an integrated set of characteristics affecting locomotion and endothermy. The major features of this hypothesis are as follows. (1) Selection for continuous, steady, and efficient swimming resulted in changes in body shape (the result of enlargement of the anterior myotomes, the anterior and internal shift of red muscle, and a narrowing of the caudal peduncle) which increased streamlining and led to the adoption of the thunniform swimming mode unique to the tunas. (2) Alterations in blood supply necessitated by the anterior shift in red muscle led to the interdigitation of numerous arterial and venous branches which set the stage for heat conservation. (3) The evolution of endothermy, together with thunniform swimming, contributed significantly to the ecological radiation and diversification of tunas during the Early Tertiary Period. Our studies of A. fallai thus suggest that the shift in red muscle position and changes in central circulation preceded the evolution of red-muscle endothermy. Co-evolutionary changes in red muscle quantity and distribution and in vascular specializations for heat conservation have led to different macroevolutionary trajectories among the now five genera and 14 tuna species of tunas and appear to reflect the influence of changing paleocological and paleoceanographic conditions, including cooling, that occurred in the Tertiary.

The evolution of thunniform locomotion and heat conservation in scombrid fishes: New insights based on the morphology of Allothunnus fallai

Two significant functional differences—a more anterior and internally positioned red myoItomal muscle mass and modification of the red-muscle vascular supply to form counter-current heat exchangers—distinguish the tunas (tribe Thunnini) from other species in the teleost family Scombridae. Neither of these characteristics is found in the bonitos (tribe Sardini), the sister group to the Thunnini. The most recent scombrid classification places the slender tuna, Allothunnus fallai, in the tribe Sardini, but some earlier studies suggested that this species should be a member of the Thunnini. Allothunnus fallai does not possess the lateral subcutaneous arteries and veins or the lateral heat-exchanging retia typical of tunas. However, we have found that this species has a highly modified central circulation (dorsal aorta, post cardinal vein, and associated branch vessels) similar to the central heat-exchanging retia of certain tunas, an enlarged haemal arch to accommodate this structure, and the anterior, internal placement of red muscle characteristic of tunas. With these new characters, phylogenetic reconstructions based on parsimony place A. fallai as the sister taxon to the tunas, establish that it is the most basal tuna species, and support the hypothesis that the derivation of tunas from a bonito-like ancestor occurred through selection for an integrated set of characteristics affecting locomotion and endothermy. The major features of this hypothesis are as follows. (1) Selection for continuous, steady, and efficient swimming resulted in changes in body shape (the result of enlargement of the anterior myotomes, the anterior and internal shift of red muscle, and a narrowing of the caudal peduncle) which increased streamlining and led to the adoption of the thunniform swimming mode unique to the tunas. (2) Alterations in blood supply necessitated by the anterior shift in red muscle led to the interdigitation of numerous arterial and venous branches which set the stage for heat conservation. (3) The evolution of endothermy, together with thunniform swimming, contributed significantly to the ecological radiation and diversification of tunas during the Early Tertiary Period. Our studies of A. fallai thus suggest that the shift in red muscle position and changes in central circulation preceded the evolution of red-muscle endothermy. Co-evolutionary changes in red muscle quantity and distribution and in vascular specializations for heat conservation have led to different macroevolutionary trajectories among the now five genera and 14 tuna species of tunas and appear to reflect the influence of changing paleocological and paleoceanographic conditions, including cooling, that occurred in the Tertiary.

Ecology and Evolution of Physiological Time in Insects

The fact that development rate of insects changes with temperature implies that the rate at which time passes for a developing insect depends upon the temperature regime it experiences. Understanding this so-called physiological time is of the utmost importance in explaining adaptations of insect life histories to resources that vary seasonally. This paper summarizes data on development rate for 54 species of insects and data on annual temperature regimes on an elevational and a latitudinal gradient. It then treats the curve representing temperature-dependent development as a filter of the temperature regimes during various seasons. The analysis points out several new evolutionary consequences of the position and shape of the development rate curve in relation to season and location. (1) If the criterion for maximizing fitness is fastest development accumulation, the optimal development curve can be specified. (2) In locations with high midsummer temperatures selection could favor different development curves in spring and summer and lead to polymorphism or species replacement in these seasons. (3) If the criterion is appropriate timing, some interesting possibilities emerge. (a) The importance of host-plant choice by a phytophageous insect may depend on season in locations with hot summers. (b) Development rate curves that appear to give equivalent timing at one season may actually lead to opposite responses to year-to-year changes in the temperature regime and to very different timings in different seasons. (c) Interactions between species which have temperature-dependent development rates may lead to coevolutionary changes in their respective development curves. (4) Selection along elevational and latitudinal gradients may lead to clinal variation in the development rate curve or to species replacement.