The last eukaryote common ancestor (LECA) possessed mitochondria and all key traits that make eukaryotic cells more complex than their prokaryotic ancestors, yet the timing of mitochondrial acquisition and the role of mitochondria in the origin of eukaryote complexity remain debated. Here we report evidence from gene duplications in LECA indicating an early origin of mitochondria. Among 163,545 duplications in 24,571 gene trees spanning 150 sequenced eukaryotic genomes, we identify 713 gene duplication events that occurred in LECA. LECA's bacterial derived genes include numerous mitochondrial functions and were duplicated significantly more often than archaeal derived and eukaryote specific genes. The surplus of bacterial derived duplications in LECA most likely reflects the serial copying of genes from the mitochondrial endosymbiont to the archaeal host's chromosomes. Clustering, phylogenies and likelihood ratio tests for 22.4 million genes from 5,655 prokaryotic and 150 eukaryotic genomes reveal no evidence for lineage specific gene acquisitions in eukaryotes, except from the plastid in the plant lineage. That finding, and the functions of bacterial genes duplicated in LECA, suggest that the bacterial genes in eukaryotes are acquisitions from the mitochondrion, followed by vertical gene evolution and differential loss across eukaryotic lineages, flanked by concomitant lateral gene transfer among prokaryotes. Overall, the data indicate that recurrent gene transfer via the copying of genes from a resident mitochondrial endosymbiont to archaeal host chromosomes preceded the onset of eukaryotic cellular complexity, favoring mitochondria-early over mitochondria-late hypotheses for eukaryote origin.

The first annotated checklist of crickets and grasshoppers (Orthoptera) of Croatia is presented. With 184 orthopteran species, 103 Ensifera and 81 Caelifera, known to inhabit the country, Croatia is among the richest European countries in terms of Orthoptera diversity. Altogether 25 species erroneously reported from the country are omitted from the checklist, 16 Ensifera (Isophya speciosa, Poecilimon brunneri, P. jonicus, P. thoracicus, Modestana ebneri, Pachytrachis bosniacus, Rhacocleis neglecta, Tessellana carinata, T. nigrosignata, Zeuneriana marmorata, Pteronemobius lineolatus, Myrmecophilus acervorum, M. ochraceus, Dolichopoda palpata, Diestrammena asynamora, Troglophilus brevicauda) and 9 Caelifera (Tetrix kraussi, Paracaloptenus caloptenoides, Chorthippus albomarginatus, Omocestus viridulus, Pseudochorthippus montanus, Miramella alpina, Celes variabilis, Oedipoda germanica, O. miniata). First faunistic records of 10 taxa are reported for Croatia, in total four Ensifera (Leptophyes punctatissima, Metrioptera hoermanni, Zeuneriana amplipennis, Gryllotalpa sp.) and six Caelifera (Xya variegata, Chorthippus dichrous, C. loratus, C. mollis ignifer, Odontopodisma sp., Acrotylus l. longipes). For each listed species, its distribution in Croatia and in Europe is given, and IUCN European Red List status is shown for species within threatened categories. Numerous distributional, taxonomic and nomenclatural problems are discussed. Several taxa with poorly defined diagnostic traits are synonymized, namely Gampsocleis abbreviata renei syn.nov. (with G. a. abbreviata), Pholidoptera maritima syn.nov. (with P. dalmatica), P. brachynota syn.nov. (with P. dalmatica), Acrida m. mediterranea syn.nov. (with A. u. ungarica), Chrysochraon dispar intermedius syn.nov. (with C. d. giganteus) and Odontopodisma rammei syn.nov. (with O. fallax).

This review examines the ecological, economical, and public health significance of chironomids and provides examples of chironomid invasions via international shipping and the subsequent local and regional impacts. Dispersal and adaptation mechanisms as facilitators of chironomid invasions are presented, and control methods are discussed. Impacts ranged from increased nuisance occurrences to agricultural disruption. Anthropogenic activities including pollution-related decimation of aquatic benthic communities might allow introduction of invasive chironomids. Chironomids can inhabit many environments, including eutrophic lakes and wastewater treatment areas, and may accumulate contaminants in high concentrations. Health concerns include the association of chironomid egg masses with Vibrio cholerae, roles of chironomids as vectors for avian botulism, and effects of chironomid chemicals as human allergens. Therefore, the presence of new chironomid species in an environment may present threats to public health and local ecosystems.

Modern accounts of eukaryogenesis entail an endosymbiotic encounter between an archaeal host and a proteobacterial endosymbiont, with subsequent evolution giving rise to a unicell possessing a single nucleus and mitochondria. The mononucleate state of the last eukaryotic common ancestor, LECA, is seldom, if ever, questioned, even though cells harboring multiple (syncytia, coenocytes, polykaryons) are surprisingly common across eukaryotic supergroups. Here we present a survey of multinucleated forms. Ancestral character state reconstruction for representatives of 106 eukaryotic taxa using 16 different possible roots and supergroup sister relationships, indicate that LECA, in addition to being mitochondriate, sexual, and meiotic, was multinucleate. LECA exhibited closed mitosis, which is the rule for modern syncytial forms, shedding light on the mechanics of its chromosome segregation. A simple mathematical model shows that within LECA’s multinucleate cytosol, relationships among mitochondria and nuclei were neither one-to-one, nor one-to-many, but many-to-many, placing mitonuclear interactions and cytonuclear compatibility at the evolutionary base of eukaryotic cell origin. Within a syncytium, individual nuclei and individual mitochondria function as the initial lower-level evolutionary units of selection, as opposed to individual cells, during eukaryogenesis. Nuclei within a syncytium rescue each other’s lethal mutations, thereby postponing selection for viable nuclei and cytonuclear compatibility to the generation of spores, buffering transitional bottlenecks at eukaryogenesis. The prokaryote-to-eukaryote transition is traditionally thought to have left no intermediates, yet if eukaryogenesis proceeded via a syncytial common ancestor, intermediate forms have persisted to the present throughout the eukaryotic tree as syncytia, but have so far gone unrecognized.