Surveillance of avian malaria and related haemoparasites in common terns (Sterna hirundo) on the Atlantic coast of South America.

Haemosporidia (Apicomplexa, Haemosporida) are protozoa that infect vertebrate blood cells and are transmitted by vectors. Among vertebrates, birds possess the greatest diversity of haemosporidia, historically placed in 3 genera: Haemoproteus, Leucocytozoon and Plasmodium, the causative agent of avian malaria. In South America, existing data on haemosporidia are spatially and temporally dispersed, so increased surveillance is needed to improve the determination and diagnosis of these parasites. During the non-breeding season in 2020 and 2021, 60 common terns (Sterna hirundo) were captured and bled as part of ongoing research on the population health of migratory birds on the Argentinian Atlantic coast. Blood samples and blood smears were obtained. Fifty-eight samples were screened for Plasmodium, Haemoproteus and Leucocytozoon, as well as for Babesia parasites by nested polymerase chain reaction and by microscopic examination of smears. Two positive samples for Plasmodium were found. The cytochrome b lineages detected in the present study are found for the first time, and are close to Plasmodium lineages found in other bird orders. The low prevalence (3.6%) of haemoparasites found in this research was similar to those reported for previous studies on seabirds, including Charadriiformes. Our findings provide new information about the distribution and prevalence of haemosporidian parasites from charadriiforms in the southernmost part of South America, which remains understudied.

Phylogenetic relationship between Contracaecum spp. (Nematoda, Anisakidae) parasitizing cormorants (Aves, Phalacrocoracidae) in Argentina.

Species of the genus Contracaecum (Family Anisakidae) exhibit a broad host and geographical distribution, parasitizing aquatic organisms such as piscivorous birds and mammals as their definitive hosts. Several Contracaecum species have been reported parasitizing cormorants (Family: Phalacrocoracidae) in South America. The objective of this study was to highlight phylogenetic relationships between Contracaecum species parasitizing cormorants based on both molecular analyses and the papillae arrangement on the male tail. Some Contracaecum species parasitizing Red-legged cormorants from the Ría Deseado (RD), and other nematodes parasitizing eight Neotropic cormorants from San Miguel del Monte lagoon (SMML), Argentina, were collected and analyzed. Both morphological and phylogenetic analyses allowed us to recognize two species: Contracaecum chubutensis parasitizing Phalacrocorax gaimardi, and Contracaecum australe parasitic in Phalacrocorax brasilianus. According to the obtained sequences (mtDNA cox2, ITS1, ITS2, and SSrRNA), Contracaecum sp. parasitizing P. gaimardi exhibited concordance with the previously reported C. chubutensis parasitizing P. atriceps from Bahía Bustamante, Chubut province. Likewise, Contracaecum sp. isolates parasitizing P. brasilianus showed concordance with C. australe from Chile. Besides, the papillae arrangement on the male tail allowed us to understand the interspecific and genetic relationships between the Contracaecum species. The analyses confirm that C. chubutensis specimens parasitizing P. gaimardi from RD present a new host record for the species, whereas, those C. australe specimens parasitizing P. brasilianus from SMML provide a new geographical record for the species and the extension of its distribution range. Present results also confirm the inland and marine distribution of C. australe and C. chubutensis, respectively.

Parasitological survey of coastal birds from the Magellanic coast, Southwestern Atlantic Ocean.

Ecto and endoparasites of four species of coastal birds, Haematopus ater, Larus dominicanus, Leucophaeus scoresbii (Charadriiformes), and Lophonetta specularioides (Anseriformes), are reported from Puerto Deseado on the Patagonian coast, Argentina. Only H. ater was infested with lice (Phthiraptera), belonging to 2 species (Ischnocera, Amblycera). A total of 19 helminth species were found parasitizing the coastal birds studied: 4 cestodes (1 Tetrabothriidae, 3 Cyclophyllidea); 11 trematodes (2 Gymnophallidae, 3 Microphallidae, 2 Notocotylidae, 1 Philophthalmidae, 2 Renicolidae, 1 Schistosomatidae); 3 nematodes (1 Anisakidae, 2 Acuariidae); and 1 acanthocephalan (Polymorphidae). Although some isolated records have been previously reported for these birds, the present work provides a parasitofauna study for H. ater, L. scoresbii, and L. specularioides for the first time. Endoparasites reflected the feeding habits of the birds; the parasite assemblage of L. dominicanus was the richest, indicating their wide prey spectrum and the diversity of the habitats frequented. A great species richness of trematodes, whose life cycles are partially known, suggests that L. specularioides feeds upon crustaceans and small bivalves. The blackish oystercatcher H. ater preys upon the limpet Nacella magellanica which hosts two larval trematodes corresponding to the adults found parasitizing it.

Update of Dicrocoeliidae (Digenea) parasitizing rodents from the Americas with a description of a new Platynosomoides species from Argentina.

Digeneans are common parasites of small mammals. Dicrocoeliidae is a family with a cosmopolitan distribution, with 18 genera previously recorded from mammals in the Americas, six of them parasitizing rodents in Argentina. In this study, an updated compilation is provided of Dicrocoeliidae from rodents in the Americas. Also, a new Platynosomoides species is described parasitizing the cricetid rodent Akodon montensis of the Atlantic Forest in Argentina. Digital repositories were used to search for Dicrocoeliidae from rodents in the Americas. Rodents were collected in four localities of the Atlantic Forest, Argentina. Digeneans were removed from the rodent's bile duct, and conventional studies were used for the morphological description. A total of 15 Dicrocoeliidae species were found parasitizing 18 rodent species from eight countries in the Americas. The new species of Platynosomoides from Akodon montensis differs from the other two species of genus by the size of body, testes, ovary, cecum length and position and length of the vitelline bands. Dicrocoeliidae show growing diversity, and the compilation of species in a rodent host base allows a clearer comparison and identification of new taxa in the future.

Redescription and molecular characterization of Baruscapillaria spiculata (Nematoda: Capillariidae) parasitizing the Neotropic cormorant Phalacrocorax brasilianus from two Argentinian lagoons.

Two species of intestinal Capillariidae were hitherto known from the Neotropic cormorant Phalacrocorax brasilianus, Baruscapillaria spiculata (Freitas, 1933), and Baruscapillaria appendiculata (Freitas, 1933). The original descriptions are very short and brief, and further reports of both species are scarce and/or confusing. This paper provides a morphological redescription and molecular characterization, based on the partial 18S rDNA gene, of B. spiculata specimens parasitizing the Neotropic cormorant in two continental lagoons from Buenos Aires province, Argentina. Both morphological and morphometrical differences between B. spiculata and B. appendiculata are highlighted on the examination of available type material. Additionally, two previous reports of B. appendiculata from Mexico and Brazil are discussed. A phylogenetic analysis conducted on specimens of B. spiculata and 46 other capillariid isolates available from the GenBank demonstrated a sister-taxon relationship between our specimens and the type species of Baruscapillaria. But, at the same time, significant genetic distances between both taxa showed an interesting variability of the genus Baruscapillaria. The probable division of this genus into multiple genera could probably be confirmed through integrative studies including more species.

Gulls as carriers of antimicrobial resistance genes in different biogeographical areas of South America.

The aim of this communication was to establish if Enterobacterales associated with gulls in Argentina harbored antimicrobial resistance (AMR) genes. We analyzed cloacal swabs in two contrasting areas: Ensenada, Buenos Aires province (26 Larus dominicanus and 22 Chroicocephalus maculipennis) and Puerto Madryn, Chubut province (20 L. dominicanus). In Ensenada, bla CTX-M and mcr-1 genes, were isolated from both gull species, whereas in the Puerto Madryn, only bla CTX-M gene was found. We report for the first time C. maculipennis as carrier of AMR. The finding of AMR in wildlife constitutes a useful tool in evaluating the anthropogenic impact on environmental health.

Angiostrongylus spp. in the Americas: geographical and chronological distribution of definitive hosts versus disease reports.

BACKGROUND: Angiostrongyliasis is an infection caused by nematode worms of the genus Angiostrongylus. The adult worms inhabit the pulmonary arteries, heart, bronchioles of the lung, or mesenteric arteries of the caecum of definitive host. Of a total of 23 species of Angiostrongylus cited worldwide, only nine were registered in the American Continent. Two species, A. cantonensis and A. costaricensis, are considered zoonoses when the larvae accidentally parasitise man. OBJECTIVES: In the present study, geographical and chronological distribution of definitive hosts of Angiostrongylus in the Americas is analysed in order to observe their relationship with disease reports. Moreover, the role of different definitive hosts as sentinels and dispersers of infective stages is discussed. METHODS: The study area includes the Americas. First records of Angiostrongylus spp. in definitive or accidental hosts were compiled from the literature. Data were included in tables and figures and were matched to geographic information systems (GIS). FINDINGS: Most geographical records of Angiostrongylus spp. both for definitive and accidental hosts belong to tropical areas, mainly equatorial zone. In relation to those species of human health importance, as A. cantonensis and A. costaricensis, most disease cases indicate a coincidence between the finding of definitive host and disease record. However, in some geographic site there are gaps between report of definitive host and disease record. In many areas, human populations have invaded natural environments and their socioeconomic conditions do not allow adequate medical care. MAIN CONCLUSIONS: Consequently, many cases for angiostrongyliasis could have gone unreported or unrecognised throughout history and in the nowadays. Moreover, the population expansion and the climatic changes invite to make broader and more complete range of observation on the species that involve possible epidemiological risks. This paper integrates and shows the current distribution of Angiostrongylus species in America, being this information very relevant for establishing prevention, monitoring and contingency strategies in the region.

Morphological and molecular evidence on the existence of a single estuarine and rocky intertidal acanthocephalan species of Profilicollis Meyer, 1931 (Acanthocephala: Polymorphidae) along the Atlantic and Pacific coasts of southern South America.

Profilicollis chasmagnathi Holcman-Spector, Mañé-Garzón & Dei-Cas, 1977 (Acanthocephala: Polymorphidae) has been reported to parasitise different grapsid species as intermediate hosts along the South Atlantic shores, i.e. Cyrtograpsus angulatus (Dana) and Neohelice granulata (Dana) in Uruguay and Cyrtograpsus altimanus (Rathbun) in Argentina. Larvae of a similar acanthocephalan described as Profilicollis antarcticus Zdzitowiecki, 1985 were recorded in the crab Hemigrapsus crenulatus (Milne-Edwards) from an estuarine habitat on the Southeast Pacific shore in Chile. Earlier studies have questioned the specific assignation of the Chilean estuarine populations of Profilicollis Meyer, 1931. The aim of this study was to re-examine the identification of these acanthocephalans by means of morphological and molecular analyses of cystacanths of Profilicollis spp. gathered from C. angulatus, N. granulata, C. altimanus and H. crenulatus. Our analyses showed that a single species of Profilicollis, P. chasmagnathi, parasitises these four crab species. The assessment of specimens from the South Shetlands Islands, the type-locality of P. antarcticus, is needed before formally proposing that P. antarcticus is a junior subjective synonym of P. chasmagnathi.

The genus Contracaecum Raillet & Henry (Nematoda: Anisakidae): host and geographical distribution on Neotropical and Antarctic species.

Nematodes of the genus Contracaecum Raillet & Henry, 1912 (Anisakidae, Contracaecinae) have a worldwide distribution. The taxonomy of the genus Contracaecum is well-known nowadays due to several morphometric studies, scanning electron microscopy, and molecular biology. The aim of this work was to review, clarify, and summarize the valid species of the genus Contracaecum parasitizing piscivorous sea birds and mammals from both the Neotropical and Antarctic regions reviewing all scientific available papers and electronic searching data up to date. A checklist on Neotropical and Antarctic Contracaecum spp. was organized through a revision of scientific papers and original descriptions. The systematic online search and the most updated papers were obtained through SCOPUS, Google Scholar, PubMed, Medline, World Register of Marine Species, etc. We provide information about hosts, Neotropical and Antarctic localities where worms were collected, references, molecular markers, and Genbank accession numbers. Twenty-five Neotropical and Antarctic Contracaecum species have been recorded up to date and checked out as valid ones according to the most updated data. Twenty-one species parasitize exclusively fish-eating birds, two species were reported only on marine mammals, and the other two parasitize both sea birds and mammals. A total of 20 Contracaecum species are exclusively reported for the Neotropical region, three only for Antarctic hosts, and two species were reported parasitizing both Neotropical and Antarctic hosts. Several Contracaecum species (10) have been corroborated by molecular analysis of different genetic markers. After reviewing all morphological descriptions of the Contracaecum species, and despite most of them have been characterized only by morphometric methods, we are convinced that all species listed in this work correspond to good and valid Contracaecum Neotropical and Antarctic species. Present results indicate that more taxonomic and molecular studies are needed to advance the understanding of the distribution and host specificity of the Contracaecum species.

Morphological, molecular and histopathological characterization of Plagiorhynchus crassicollis (Acanthocephala: Plagiorhynchidae) from a neotropical shorebird in Patagonia, Argentina.

In this work we report Plagiorhynchus (Plagiorhynchus) crassicollis from Patagonia, Argentina. Specimens were collected from the small intestine of a charadriid shorebird with Neotropical distribution, the Two-banded Plover (Charadrius falklandicus). Both morphological and molecular characterization, plus pathological aspect of this species is provided. Plagiorhynchus (Plagiorhynchus) crassicollis is characterized by having a proboscis with 18-20 longitudinal rows of hooks and 11-14 hooks per row. Sequences of the small subunit (SSU) and large subunit (LSU) of the nuclear ribosomal DNA were obtained and compared with other sequences available in GenBank. Phylogenetic analyses inferred with each molecular marker consistently showed that P. (P.) crassicollis is sister taxa to Plagiorhynchus (Plagiorhynchus) aznari, a parasite of the long-billed curlew (Numenius americanus) from northern Mexico. Pathologic findings associated with the parasites include ulcerative enteritis, granulomatous inflammation, diffuse lymphocytic infiltration, serositis, and peritonitis. This record expands the host and geographical record of P. (P.) crassicollis, provide baseline information on its pathological aspects, and represents the first molecular characterization of P. crassicollis in the Neotropics.

Risk assessment of SARS-CoV-2 in Antarctic wildlife.

The coronavirus disease 2019 (COVID-19) pandemic is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This pathogen has spread rapidly across the world, causing high numbers of deaths and significant social and economic impacts. SARS-CoV-2 is a novel coronavirus with a suggested zoonotic origin with the potential for cross-species transmission among animals. Antarctica can be considered the only continent free of SARS-CoV-2. Therefore, concerns have been expressed regarding the potential human introduction of this virus to the continent through the activities of research or tourism to minimise the effects on human health, and the potential for virus transmission to Antarctic wildlife. We assess the reverse-zoonotic transmission risk to Antarctic wildlife by considering the available information on host susceptibility, dynamics of the infection in humans, and contact interactions between humans and Antarctic wildlife. The environmental conditions in Antarctica seem to be favourable for the virus stability. Indoor spaces such as those at research stations, research vessels or tourist cruise ships could allow for more transmission among humans and depending on their movements between different locations the virus could be spread across the continent. Among Antarctic wildlife previous in silico analyses suggested that cetaceans are at greater risk of infection whereas seals and birds appear to be at a low infection risk. However, caution needed until further research is carried out and consequently, the precautionary principle should be applied. Field researchers handling animals are identified as the human group posing the highest risk of transmission to animals while tourists and other personnel pose a significant risk only when in close proximity (< 5 m) to Antarctic fauna. We highlight measures to reduce the risk as well as identify of knowledge gaps related to this issue.

Redescription of Ingliseria cirrohamata (Linstow, 1888) (Nematoda: Acuariidae), including new hosts and geographical records.

Inglisera cirrohamata (Linstow, 1888) (Nematoda: Acuariidae) is redescribed based on specimens collected from the type host, Phalacrocorax verrucosus (Aves: Phalacrocoracidae), and the type locality, Kerguelen Island, in the southern Indian Ocean. Three new hosts and 2 new localities were recorded, i.e., Phalacrocorax [atriceps] albiventer and P. brasilianus from Puerto Madryn, Argentina and P. magellanicus from Puerto Williams, Chile. The structure of the cephalic ornamentations was observed and fully described. The presence of 6 pairs of postcloacal papillae is confirmed, a description of the tip of left spicule is given, and the presence of post-deirids is reported for the first time. This constitutes the first record of this nematode in South America and provides the first study of the genus by scanning electron microscopy.

Species of Contracaecum Parasitizing the Magellanic Penguin Spheniscus magellanicus (Spheniscidae) from the Argentinean Coast.

Anisakid nematodes have a worldwide distribution and are associated with fishes, birds, and marine mammals from freshwater, brackish, and marine systems. The aims of this work are to report for the first time Contracaecum mirounga parasitizing the Magellanic penguin Spheniscus magellanicus, to report another Contracaecum species in the same host species, and to discuss the validity of Contracaeceum spheniscus. Several dead chicks, juveniles, and adults of S. magellanicus were collected along the Argentinean coast from 2002 to 2009. Nematodes were removed from digestive tracts and studied using both light and scanning electron microscopy. Nematode prevalences were 2.38% for C. mirounga and 12.5% for Contracaecum sp. Contracaecum mirounga was found in 1 penguin from Península Valdés, Chubut. This species is known as a specific parasite of marine mammals such as Pinnipedia, thereby suggesting that this nematode is not as specific as believed. Another species of Contracaecum sp. was found parasitizing 1 penguin from the Río de la Plata coast. It possessed an unusual interlabial morphology and arrangement of male caudal papillae. Despite the low prevalence, the distinct morphological features are convincing and support the presence of a new Contracaecum species. However, a formal description is not presented because sufficient male specimens are lacking. Finally, C. spheniscus is considered a junior synonym of Contracaecum pelagicum. Future molecular studies might be helpful to determine the real diversity of Contracaecum species parasitizing S. magellanicus considering the number of sibling species recognized among the anisakids.

A new species of Maritrema (Trematoda: Microphallidae) parasitizing the Baird's sandpiper Calidris bairdii, and comments about diversity of Microphallidae in two Nearctic shorebirds at Patagonian sites in Argentina.

Birds are hosts of a wide diversity of trematodes. Between them, the Microphallidae is a common family with a cosmopolitan distribution. Nevertheless, only 10 Maritrema species have been recorded previously in South America. The aim of the present paper is to describe a new species of Maritrema parasitizing the Nearctic Baird's sandpiper, Calidris bairdii in its wintering areas in Patagonia, Argentina. We also analyze and compare the microphallid diversity in two host species. We collected 44 C. bairdii and 50 Calidris fuscicollis in search of helminths. Trematodes were found only in C. bairdii. A total of 694 trematodes belonging to 4 microphallid species were found parasitizing the intestine and caeca. Four microphallid species were found: Maritrema formicae, Odhneria odhneri, Levinseniella cruzi and Maritrema pichi n. sp. M. formicae showed the highest prevalence, while M. pichi n. sp. was the species with the highest mean intensity and mean abundance. The new species M. pichi n. sp. differs from congeners by the position of the acetabulum that is included within the vitellarium ring, the ovary is anterior to the acetabulum, and the testes are lateral to it. We discuss the parasitological results in relation with the biological and ecological characteristics of both different host species.

A new anisakid species parasitizing the imperial cormorant Phalacrocorax atriceps from the North Patagonian Coast, Argentina.

The anisakid species Contracaecum chubutensis n. sp. was found parasitizing the imperial cormorant Phalacrocorax atriceps at 2 different localities, Bahía Bustamante (45 degrees 11'S, 66 degrees 30'W) and Puerto Madryn (42 degrees 47'S, 65 degrees 02'W) on the Patagonian coast. Morphometrical analysis and further studies of adult specimens of C. chubutensis n. sp. and fourth-stage larvae of Contracaecum sp. were done using light and scanning electron microscopy. The possession and disposition of 7 pairs of tail papillae differentiate this new species from C. osculatum, C. radiatum, C. plagiaticium, and C. mirounga. Double-sized spicules separate it from C. variegatum and C. pelagicum. Moreover, the paracloacal papillae disposition and tail shape differentiate this new species from C. travassosi. The presence of bifurcated interlabia separate it from C. ogmorhini and C. margolisi. Three well-marked lip notches, a sharp tail shape, and the of the transversal paracloacal papillae disposition distinguishes C. chubutensis n. sp. from C. magnipapillatum and C. septentrionale. The species here described can be differentiated from C. caballeroi by its bifurcated interlabia, longer spicules, and for possessing more precloacal papillae pairs. It can be separated from C. rudolphii by a thinner interlabia at the base, deeper lip notches, a sharper tail, the disposition of transversal paracloacal papillae, and greater distance between both papillae of the first subventral distal papillae pair. In addition, fourth-stage larvae recovered from the same host and localities were identified and described as Contracaecum sp. Prevalence of adult parasites was 66.7 %, mean intensity was 4.0, and mean abundance was 7.1.

Life Cycle of the Parasite Profilicollis chasmagnathi (Acanthocephala) On the Patagonian Coast of Argentina Based On Morphological and Molecular Data.

This study verifies the identity of adult specimens of the parasite Profilicollis chasmagnathi (Acanthocephala, Polymorphidae) recovered from kelp gulls Larus dominicanus (Aves, Laridae), and cystacanths found in crabs Cyrtograpsus altimanus (Crustacea, Decapoda) from the southwestern Atlantic coast. The life cycle of this parasite is elucidated in the intertidal zone of Patagonia, Argentina, based on morphological and molecular data. Preferences by size and sex of the intermediate host and seasonal variation of this parasite are provided, contributing to the knowledge of this host-parasite association.

A new genus and species of acuarioid nematode (Acuariidae: Seuratiinae) in petrels Pterodroma externa and P. neglecta from the Juan Fernández Islands, Chile.

A new genus and species of Seuratiinae is described based on adults recovered from the Juan Fernández and Kermedec Petrels (Pterodroma externa and P. neglecta) from the Juan Fernández Islands of Chile (south Pacific). Navonia pterodromae n. gen., n. sp. is distinguished from the other genera and species in Seuratiinae by the combination of the following characters: (1) cordons arising from commissures of buccal lips originating a finely denticulate collarette divided into 2 lateral lobes, and detached from underlying cuticle; (2) inconspicuous simple to bicuspid deirids; (3) presence of area rugosa; and (4) presence of a large left spicule in the male. It is also distinguished from some genera and species in this subfamily by the presence of a lateral furrow. Seuratia shipleyi was also recorded from P. externa. These are the first records of helminths in these 2 hosts and the first records of Seuratiinae from Chile.

Further study of Contracaecum pelagicum (Nematoda: Anisakidae) in Spheniscus magellanicus (Aves: Spheniscidae) from Argentinean coasts.

The anisakid species Contracaecum pelagicum Johnston and Mawson, 1942, is reported for first time at 2 different sites on the Argentine coast (Peninsula Valdés, 42 degrees 04'S, 63 degrees 38'W and Mar del Plata, 38 degrees 05'S, 57 degrees 38'W), parasitizing the Magellanic penguin, Spheniscus magellanicus Foster. Morphometric analysis and further studies of adult specimens of C. pelagicum were done using light and scanning electron microscopy. The presence of bifurcated interlabia differentiates the present species from most others in the genus, except (1) from Contracaecum travassosi, which possesses higher interlabia and longer spicules, and a blunt, more constrained tail; (2) from Contracaecum rudolphii, which has longer spicules, blunter spicule tips, postparacloacal papillae with oblique disposition, and a blunter constrained tail; (3) from Contracaecum eudyptulae, which has a blunter tail and longer spicules; and (4) from Contracaecum variegatum, which possesses smaller-diameter, hooklike extensions on auricle lips, and a less robust interlabium with a more marked furrow. In this paper we present the first detailed description of C. pelagicum adults from S. magellanicus. Morphometric data between adult specimens of C. pelagicum from S. magellanicus and those from the black-browed albatross, Diomedea melanophris Temminck, from Argentinean coasts were compared. In addition, fourth-stage larvae that parasitized both hosts were assigned to a nondeterminated Contracaecum species. Ecological parameters for adults and larvae nematodes were calculated.

Age-Related Differences in the Gastrointestinal Microbiota of Chinstrap Penguins (Pygoscelis antarctica).

The gastrointestinal tract microbiota is known to play very important roles in the well being of animals. It is a complex community composed by hundreds of microbial species interacting closely among them and with their host, that is, a microbial ecosystem. The development of high throughput sequencing techniques allows studying the diversity of such communities in a realistic way and considerable work has been carried out in mammals and some birds such as chickens. Wild birds have received less attention and in particular, in the case of penguins, only a few individuals of five species have been examined with molecular techniques. We collected cloacal samples from Chinstrap penguins in the Vapour Col rookery in Deception Island, Antarctica, and carried out pyrosequencing of the V1-V3 region of the 16S rDNA in samples from 53 individuals, 27 adults and 26 chicks. This provided the first description of the Chinstrap penguin gastrointestinal tract microbiota and the most extensive in any penguin species. Firmicutes, Bacteoridetes, Proteobacteria, Fusobacteria, Actinobacteria, and Tenericutes were the main components. There were large differences between chicks and adults. The former had more Firmicutes and the latter more Bacteroidetes and Proteobacteria. In addition, adults had richer and more diverse bacterial communities than chicks. These differences were also observed between parents and their offspring. On the other hand, nests explained differences in bacterial communities only among chicks. We suggest that environmental factors have a higher importance than genetic factors in the microbiota composition of chicks. The results also showed surprisingly large differences in community composition with other Antarctic penguins including the congeneric Adélie and Gentoo penguins.