Bennettitales, Erdtmanithecales and Gnetales from the Early Cretaceous of the Lusitanian Basin (western Portugal)

This paper presents a synthesis of the occurrence of extinct gymnosperms related to the Bennettitales, Erdtmanithecales and Gnetales group and discusses the stratigraphic setting of previously described specimens. These plants are represented by small fossil seeds collected from Lower Cretaceous (Berriasian to Lower Albian) fluvial siliciclastic deposits of the Lusitanian Basin, western Portugal, and probably constitute a monophyletic group, the BEG complex. The fossil seeds are composed of an innermost membranous nucellus preserved as a delicate cuticle. The nucellus is evolved by a membranous integument surrounded by a sclerenchymatic outer envelope. Plants from the BEG complex were contemporary of the earliest angiosperm having shared ecosystems with similar environmental characteristics, what reinforces its paleoecological importance

The last bastion? X-chromosome genotyping of Anopheles gambiae species-pair males from a hybrid zone reveals complex recombination within the major candidate ‘genomic island of speciation’

Speciation with gene flow may be aided by reduced recombination helping to build linkage between genes involved in the early stages of reproductive isolation. Reduced recombination on chromosome-X has been implicated in speciation within the Anopheles gambiae complex, species of which represent the major Afrotropical malaria vectors. The most recently diverged, morphologically-indistinguishable, species-pair, An. gambiae and An. coluzzii, ubiquitously display a ‘genomic island of divergence’ spanning over 4Mb from chromosome-X centromere, which represents a particularly promising candidate region for reproductive isolation genes, in addition to containing the diagnostic markers used to distinguish the species. Very low recombination makes the island intractable for experimental recombination studies, but an extreme hybrid zone in Guinea Bissau offers the opportunity for natural investigation of X-island recombination. SNP-analysis of chromosome-X hemizygous males revealed: (i) strong divergence in the X-island despite a lack of autosomal divergence; (ii) individuals with multiple-recombinant genotypes, including likely double crossovers and localized gene conversion; (iii) recombination-driven discontinuity both within and between the molecular species markers, suggesting that the utility of the diagnostics is undermined under high hybridization. The largely-, but incompletely-protected nature of the X-centromeric genomic island is consistent with a primary candidate area for accumulation of adaptive variants driving speciation with gene flow, whilst permitting some selective shuffling and removal of genetic variation

Stratigraphy and allogenic controls of the western Portugal Cretaceous: an updated synthesis

The stratigraphy of the western Portugal on-shore Cretaceous record (western Iberian margin, Lusitanian Basin) is described, including formal units and a selection of informal units prevailing in the geological literature. This paper is a synthesis based on a review of previous works, but with an innovative emphasis on the interpretation of eustatic and tectonic controls. The sedimentary record is dominated by siliciclastics and comprises fluvial and deltaic coastal marine siliciclastic systems, as well as extensive deposits of shallow marine carbonate platforms, both open and rimmed. Several regional unconformities and transgressive/regressive cycles are identified and the allogenic controls interpreted, namely the geodynamic events along the boundaries of the Iberian plate. Above the Berriasian deposits belonging to the Upper Jurassic cycle, the five main unconformity-bounded units are: (1) upper Berriasian–lower Barremian, (2) upper Barremian–lower Aptian, (3) upper Aptian–uppermost Cenomanian, (4) mid lower Turonian–lower Campanian and (5) middle Campanian–Maastrichtian. These units show transgressive peaks in the lower Hauterivian, lower Aptian, base of the upper Cenomanian and mid lower Turonian. The general trend of the Lower Cretaceous reflects the transition from late rifting to passive margin, with the last break-up unconformity dated as late Aptian. The Lusitanian Basin achieved full infill by the Cenomanian, when a large carbonate platform extended far inland. The later deposits were preserved only in the northern sector and the accompanying unconformities reflect transpressive intraplate stresses generated in boundaries of the plate with Africa and Eurasia. With very low accommodation being created throughout the Late Cretaceous, fluvial deposits were dominant, including a few marine levels related with eustatic rises in the early Turonian, the Coniacian, the early Campanian and the Maastrichtian