Elevated Rates and Richness Of Insect Damage From Paleogene Argentina: Implications For Modern Neotropical Diversity

LABANDEIRA CONRAD; IGLESIAS ARI; ZARZETI LAURA; WILF PETER; JOHNSON KIRK; CÚNEO RUBEN

Bilbao

Congreso; Internacional Meeting Climate and Biota of the Early Paleogene; 2006

Internacional Meeting Climate and Biota of the Early Paleogene

Patagonian South America hosts some of the most important Southern Hemisphere middle Lattitude floras for assessing the extent of plant-insect associational relationships during the Paleogene. Floras studied  here originate from Chubut Province in Argentina, and consist of two major sites, (1) Salamanca Formation, consisting of the Ormachea Reserve (OR) and Palacios de los Loros (PL) localities in south-central Chubut Province and dated at ~61.7 Ma (Danian-Selandian boundary) based on a variety of foraminiferal zonation, paleomagnetic position and less reliable K-Ar dates; and (2) Laguna del Hunco (LH), in northwestern Chubut, comprising four major localities, LH-2, LH-4, LH-6 and LH-13, and dated at 51.91 ± 0.22 Ma (mid Ypresian, early Eocene climatic optimum) based on highly resolved Ar-Ar analyses. These two localities are complemented by a third and westernmost site, Río Pichileufú (RP) in adjacent Río Negro Province to the north, dated at 47.46 ± 0.05 Ma (early Lutetian), for which plant-insect associations currently are being compiled. The Salamanca sites represent a relative cooler warm-temperate climate by comparison to the significantly warmer Laguna del Hunco sites. Salamanca and LH both have conspicuously high levels of both overall and specialized damage exceeding any contemporaneous samples we have studied from Western North America, and LH demonstrates exceptionally high leaf-mine richness. Damage type (DT) diversity ranges from 34 (OR) and 40 (PL) for the Salamanca sites to 21 to 30 for the four LH sites, all of which are allocated to four functional feeding groups: external foliage feeding, piercing-and-sucking, galling and leaf mining. Significant examples of oviposition are not included in this analysis, and there are no clear examples of seed predation. Many stereotyped, host-specialized associations are present, particularly galls and mines, some of which illustrate the biogeographical affinities of  the total ensemble of Patagonian associations. An intriguing Gondwanan association is a frass laden blotch mine (DT88) on a Podocarpus leaf (TY10) at LH-6, identifiable to either a gracillariid or plutellid moth clade, both basal ditrysian clades that extend to the Cretaceous, that currently mine similar hosts in New Zealand. Also on a Podocarpus (PL, SA18) is a probable Gondwanan association (DT116) consisting of distinctive columnar galls attached deeply to mesophyll tissues containing resinous infilling of the larval chamber, and resembling nipple galls produced extant psyllid hemipterans. A unique association on a Euphorbiaceae leaf (TY46), at LH6, that resembles similar damage today in the warm-temperate to equatorial Neotropics, is a cecidomyiid blister gall, consisting of raised and thickened epidermal tissue with 1 to 6 centrally positioned holes that probably represent parasitoid emergences (DT83). This singular association provides evidence for three trophic levels—producer, herbivore and parasitoid—within the same gall type. At LH-13 (on TY-84), and also at RP (on an unknown dicot), are distinctive but host-nonspecific leaf excisions ranging from 180° to 270° of circular arc that are assigned to leafcutter bees (Hymenoptera: Megachilidae). Other stereotyped associations and identification of plant hosts are being investigated from these sites for comparison to other Paleogene sites in North America and to the extant Neotropical and Australasian biotas. These data provide major implications for the early diversification of the South American insect fauna, including modern plant-insect associations that have Gondwanan distributions; those are endemic to the southern part of the continent, and others that have colonized more equatorial hosts. Elevated plant species diversity and plant-insect associational diversity apparently are coupled in the Patagonian Paleogene, and these two principal drivers of terrestrial biodiversity provide early glimpses into the Paleocene origin of the elevated South American diversity of today.