Photosynthetic carbon uptake by marine phytoplankton: comparison of the stable (13C) and radioactive (14C) isotope methods

The ¹⁴C and the ¹³C methods are routinely used for measuringphytoplankton production. However, few systematic comparisonsof estimates using the two approaches have been conducted. Thepresent comparison is based on 257 pairs of samples, representing1 year of monthly sampling at 10 depths in the euphotic zone.Data, obtained by the same operators following a standard protocol,were collected at three different stations on the Scotian Shelf(Northwestern Atlantic Ocean). Overall agreement between thetwo methods was good (r=0.827). However, relative differencesbetween the two sets of estimates were not randomly distributedin time and space. Three factors (photic depth, station andsampling date), identified to explain the observed differences,were included in a three-way analysis of variance (ANOVA) usingrelative differences as the covariate. Following this ANOVA,the whole set was split into three subsets. For the two subsetswhere the above identified factors did not have any significanteffect, the distribution of relative differences was narrowerthan these for the whole data set. Significant effects of thethree factors persisted for the third subset and relative differencesexhibited wide variations. Possible explanations for the observeddifferences include (i) the volume of incubation bottles, (ii)the incubation temperature and (iii) the absence of measurementsof dark uptake.     

The molecular organization of the beta-globin complex of the deer mouse, Peromyscus maniculatus

Recombinant DNA clones have been isolated that contain 80 kb of the beta-globin complex from the deer mouse, Peromyscus maniculatus. Comparisons of this complex with that from the laboratory mouse, Mus domesticus (with an order 5'-Hbby, Hbb-bhO, Hbb-bhl, Hbb-bh2, Hbb-bh3, Hbb-bl, Hbb-b2 3') highlight organizational trends in the beta-globin complex since the two species diverged. Unlike other mammals studied thus far, the deer mouse possesses three adult genes. Partial sequence analysis indicates that each of the three adult genes is intact and hence may be functional. Hybridization of one of the two Mus pseudogenes, Hbb-bh3, to genomic blots from Peromyscus reveals that it has a homologous counterpart in Peromyscus. Homologous genes to the two gamma-like Mus genes, Hbb-bhO and Hbb-bhl, are also found in Peromyscus. The strong hybridization between the Hbb-bhl genes and significant nucleotide similarity between the Hbb-bhO genes suggest that both pairs are important for the ontogeny of these mice although no known product has been identified for the Hbb-bhO genes. The presence of Hbb-bhO and Hbb-bhl in Peromyscus suggests that the duplication that created this related gene set occurred before the two lineages diverged. A single gene for Hbb-y has been isolated from Peromyscus. The adult region in Peromyscus has undergone significant divergence from the same region in Mus, having three rather than two adult genes, the acquisition of at least 15 kb of extra DNA relative to Mus, and possibly the loss of the Hbb-bh2 pseudogene. The nonadult region of the complex, in contrast, contains the same set of genes apparently distributed over the same amount of DNA as in the Mus beta- globin complex. This observation suggests that the embryonic region of the complex is more evolutionarily stable than the adult region.      

The ecology of diet expansion in a seed-feeding beetle: Pre-existing variation, rapid adaptation and maternal effects?

Most studies of insect dietary evolution suffer from limited information on the history of host use patterns; historical patterns can only be inferred from modern patterns. We examine the ecology of a recent diet breadth expansion onto an introduced host by the seed beetle, Stator limbatus, to (1) determine if pre-existing variation for survival on Chloroleucon ebano is present in natural populations of S. limbatus, and (2) test whether natural selection has resulted in local adaptation to C. ebano in a population where this host is used. Our results indicate that variation in survival on C. ebano does exist in natural populations of S. limbatus that have historically never encountered this host, providing the variation necessary for adaptation to this host. However, we found no evidence that S. limbatus have locally adapted to C. ebano. Our most interesting discovery, however, was that the use of C. ebano by S. limbatus is facilitated by non-genetic effects of parental host plant on progeny survival; parents reared on Cercidium floridum produce progeny with substantially higher survivorship on C. ebano than parents reared on Acacia greggii due to an environmentally based parental effect. We argue that such host-plant-mediated maternal effects are likely to be common and thus important for our understanding of herbivorous insect evolution and population dynamics. This paper provides one example of how an understanding of environmentally based maternal effects can provide important information on the evolution of life-history patterns observed in nature.