History, philosophy, and application of the Global Stratotype Section and Point (GSSP)

The history, philosophy, and application of the concept of the Global Stratotype Section and Point (GSSP) are reviewed. Geochronologic units defined by GSSPs serve as practical classificatory pigeonholes for the subdivision of geologic time. Accordingly, the main factor involved in the definition of GSSPs must be global correlatability. Early opposition to the GSSP concept centered around the desire for a traditional biochronologic time scale defined conceptually in terms of palaeobiological events, but such time scales are inherently unstable and thus unsuitable for the use of all geoscientists. The GSSP concept is also generally incompatible with the desire for 'natural' geochronologic boundaries. GSSPs have been defined mainly on the basis of biostratigraphic guiding criteria, but magnetic polarity reversals and chemostratigraphic and cyclostratigraphic horizons are now playing an important role. Most primary guiding criteria used to place a 'golden spike' will eventually become problematical in some way, so GSSPs should be defined so as to be correlatable by as many different lines of age-significant information as possible. The 'Global Standard Stratigraphic Age' (better renamed 'Standard Global Numerical Age') is a numerical analogue of the golden spike. Numerical definitions are currently appropriate for the formal subdivision of the Precambrian, and perhaps also for the Pleistocene/Holocene boundary. Recent suggestions to abandon chronostratigraphic terms (system, series, stage) in favor of geochronologic terms (period, epoch, age) are logically defensible, but could perpetuate the continuing confusion between various stratigraphic categories.     

Migratory and targeted flight in seasonal forms of the black bean aphid, Aphis fabae

ABSTRACT. Adult winged forms of Aphis fabae Scop., the spring migrants (fundatrigeniae; alate virginoparae), the summer migrants (alate virginoparae) and the autumn migrants (gynoparae), were flown in an automated vertical wind tunnel, with a small green target presented every 60 s. On average, targeted flight developed in the spring and summer migrants after 19 and 15 min, respectively. However, in autumn migrants targeted flight occurred after 184 min of flight. No evidence of target approach was found up to 30 min prior to this time, although some movement towards the target was observed in the 30 min before the first response of autumn migrants, suggesting that a gradual change from migratory to targeted flight occurred. No correlation was found between aphid weight and the time to first response for spring or summer migrants, but a positive correlation was found for autumn migrants. Flight patterns of autumn migrants, in the absence of a target, are described and compared with flight patterns previously reported for summer migrants.     

Host infestation patterns of the massive liana Hydrangea serratifolia (Hydrangeaceae) in a Chilean temperate rainforest

As competition from lianas reduces fitness of host trees, lianas could influence community composition and structure if potential host species differ in susceptibility to infestation. We quantified infestation frequencies of Chilean temperate rainforest tree species by the massive liana Hydrangea serratifolia (H. et A.) F. Phil (Hydrangeaceae), which climbs using adhesive adventitious roots, and examined relationships with host light requirements and stem diameter. We recorded presence or absence of H. serratifolia in a random sample of 515 trees ≥10 cm diameter. Fifty‐four per cent of trees were infested by at least one individual of H. serratifolia. Although there was significant interspecific variation in infestation frequency, this variation was not systematically related to light requirements of host tree species. Probability of infestation increased with diameter for most host tree species, and old trees were found to be infested by a wide range of liana size classes, including some stems <2 cm diameter. This evidence supports the proposal that lianas which attach by adhesive roots can colonize host stems of any size.     

Exploring myrmecophily based on the phylogenetic interrelationships of Falagonia Sharp, 1883 (Coleoptera: Staphylinidae: Aleocharinae) and allied genera

The taxonomy of Lomechusini Fleming has a complex history. Recent studies have shown that this group is polyphyletic; however, little is known about the evolutionary interrelationships among its constituent genera. The goals of the present study are to infer the phylogenetic relationships of Falagonia Sharp and closely related genera; to define the boundaries of those genera based on synapomorphic characters; and to explore the evolution of myrmecophily within the lineage. The phylogenetic analyses are based exclusively on morphological characters of adults. A total of 36 operational taxonomic units were used for the analysis. The best trees were selected based on maximum parsimony and Bayesian inference. During the parsimony reconstruction, different weighting strategies were used to recover the most robust phylogenetic hypothesis. Although minor differences were observed in the results of the different analyses, the topologies were consistent throughout. Several groups of genera proposed by Seevers (1965), such as the ‘Tetradonia’ and ‘Ecitopora’ groups, were not recovered. Thus, these may represent nonmonophyletic groups that were based on nonsynapomorphic diagnostic characters. Our analyses consistently recovered the genera Asheidium Santiago‐Jiménez, Delgadoidium Santiago‐Jiménez, Falagonia, Newtonidium Santiago‐Jiménez, Pseudofalagonia Santiago‐Jiménez, Sharpidium Santiago‐Jiménez, Tetradonia Wasmann and Thayeridium Santiago‐Jiménez, forming a monophyletic group that we have called the ‘Asheidium complex’. Falagonia mexicana Sharp shows seven autapomorphies, none of which were used to establish the genus. Based on the phylogenetic results, myrmecophily has evolved independently at least three times within the lineage. This study, based on morphological characters, is one of the first approaches towards gaining an understanding of the phylogenetic relationships within the polyphyletic tribe Lomechusini.     

Photoperiodic regulation of the development of winged gynoparae in the aphid, Aphis fabae

ABSTRACT. In uncrowded rearing conditions, determination of the winged gynopara of the Aphis fabae Scopoli is dependent upon both pre- and postnatal short days (LD 12:12). Extension of the photophase to produce longday (LD 16:8) conditions localized on the head or abdominal region, showed that during the early larval instars of the parent generation (G1) there is a maternally-controlled induction of gynoparae. However, during later stages of embryonic development the presumptive gynoparae respond directly to photoperiod through the mother's abdominal wall. During early postnatal development, presumptive gynoparae (G2) remain sensitive to photoperiodic conditions; the photoperiodic receptors lie in the head. These results are discussed with respect to possible endocrine mediators of this photoperiodically controlled polymorphism.